1. 22 Aug, 2017 1 commit
  2. 29 Jul, 2016 1 commit
  3. 01 Jul, 2016 2 commits
    • Herbert Xu's avatar
      lib/mpi: Do not do sg_virt · 127827b9
      Herbert Xu authored
      Currently the mpi SG helpers use sg_virt which is completely
      broken.  It happens to work with normal kernel memory but will
      fail with anything that is not linearly mapped.
      
      This patch fixes this by using the SG iterator helpers.
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      127827b9
    • Herbert Xu's avatar
      crypto: rsa - Generate fixed-length output · 9b45b7bb
      Herbert Xu authored
      Every implementation of RSA that we have naturally generates
      output with leading zeroes.  The one and only user of RSA,
      pkcs1pad wants to have those leading zeroes in place, in fact
      because they are currently absent it has to write those zeroes
      itself.
      
      So we shouldn't be stripping leading zeroes in the first place.
      In fact this patch makes rsa-generic produce output with fixed
      length so that pkcs1pad does not need to do any extra work.
      
      This patch also changes DH to use the new interface.
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      9b45b7bb
  4. 31 May, 2016 7 commits
    • Nicolai Stange's avatar
      lib/mpi: refactor mpi_read_from_buffer() in terms of mpi_read_raw_data() · 20b5b7f3
      Nicolai Stange authored
      mpi_read_from_buffer() and mpi_read_raw_data() do basically the same thing
      except that the former extracts the number of payload bits from the first
      two bytes of the input buffer.
      
      Besides that, the data copying logic is exactly the same.
      
      Replace the open coded buffer to MPI instance conversion by a call to
      mpi_read_raw_data().
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      20b5b7f3
    • Nicolai Stange's avatar
      lib/mpi: mpi_read_from_buffer(): sanitize short buffer printk · cdf24b42
      Nicolai Stange authored
      The first two bytes of the input buffer encode its expected length and
      mpi_read_from_buffer() prints a console message if the given buffer is too
      short.
      
      However, there are some oddities with how this message is printed:
      - It is printed at the default loglevel. This is different from the
        one used in the case that the first two bytes' value is unsupportedly
        large, i.e. KERN_INFO.
      - The format specifier '%d' is used for unsigned ints.
      - It prints the values of nread and *ret_nread. This is redundant since
        the former is always the latter + 1.
      
      Clean this up as follows:
      - Use pr_info() rather than printk() with no loglevel.
      - Use the format specifiers '%u' in place if '%d'.
      - Do not print the redundant 'nread' but the more helpful 'nbytes' value.
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      cdf24b42
    • Nicolai Stange's avatar
      lib/mpi: mpi_read_from_buffer(): return -EINVAL upon too short buffer · 7af791e0
      Nicolai Stange authored
      Currently, if the input buffer is shorter than the expected length as
      indicated by its first two bytes, an MPI instance of this expected length
      will be allocated and filled with as much data as is available. The rest
      will remain uninitialized.
      
      Instead of leaving this condition undetected, an error code should be
      reported to the caller.
      
      Since this situation indicates that the input buffer's first two bytes,
      encoding the number of expected bits, are garbled, -EINVAL is appropriate
      here.
      
      If the input buffer is shorter than indicated by its first two bytes,
      make mpi_read_from_buffer() return -EINVAL.
      Get rid of the 'nread' variable: with the new semantics, the total number
      of bytes read from the input buffer is known in advance.
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      7af791e0
    • Nicolai Stange's avatar
      lib/mpi: mpi_read_from_buffer(): return error code · 03cdfaad
      Nicolai Stange authored
      mpi_read_from_buffer() reads a MPI from a buffer into a newly allocated
      MPI instance. It expects the buffer's leading two bytes to contain the
      number of bits, followed by the actual payload.
      
      On failure, it returns NULL and updates the in/out argument ret_nread
      somewhat inconsistently:
      - If the given buffer is too short to contain the leading two bytes
        encoding the number of bits or their value is unsupported, then
        ret_nread will be cleared.
      - If the allocation of the resulting MPI instance fails, ret_nread is left
        as is.
      
      The only user of mpi_read_from_buffer(), digsig_verify_rsa(), simply checks
      for a return value of NULL and returns -ENOMEM if that happens.
      
      While this is all of cosmetic nature only, there is another error condition
      which currently isn't detectable by the caller of mpi_read_from_buffer():
      if the given buffer is too small to hold the number of bits as encoded in
      its first two bytes, the return value will be non-NULL and *ret_nread > 0.
      
      In preparation of communicating this condition to the caller, let
      mpi_read_from_buffer() return error values by means of the ERR_PTR()
      mechanism.
      
      Make the sole caller of mpi_read_from_buffer(), digsig_verify_rsa(),
      check the return value for IS_ERR() rather than == NULL. If IS_ERR() is
      true, return the associated error value rather than the fixed -ENOMEM.
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      03cdfaad
    • Nicolai Stange's avatar
      lib/mpi: mpi_read_raw_data(): fix nbits calculation · eef0df6a
      Nicolai Stange authored
      The number of bits, nbits, is calculated in mpi_read_raw_data() as follows:
      
        nbits = nbytes * 8;
      
      Afterwards, the number of leading zero bits of the first byte get
      subtracted:
      
        nbits -= count_leading_zeros(buffer[0]);
      
      However, count_leading_zeros() takes an unsigned long and thus,
      the u8 gets promoted to an unsigned long.
      
      Thus, the above doesn't subtract the number of leading zeros in the most
      significant nonzero input byte from nbits, but the number of leading
      zeros of the most significant nonzero input byte promoted to unsigned long,
      i.e. BITS_PER_LONG - 8 too many.
      
      Fix this by subtracting
      
        count_leading_zeros(...) - (BITS_PER_LONG - 8)
      
      from nbits only.
      
      Fixes: e1045992 ("MPILIB: Provide a function to read raw data into an
                           MPI")
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      eef0df6a
    • Nicolai Stange's avatar
      lib/mpi: mpi_read_raw_data(): purge redundant clearing of nbits · dfd90510
      Nicolai Stange authored
      In mpi_read_raw_data(), unsigned nbits is calculated as follows:
      
       nbits = nbytes * 8;
      
      and redundantly cleared later on if nbytes == 0:
      
        if (nbytes > 0)
          ...
        else
          nbits = 0;
      
      Purge this redundant clearing for the sake of clarity.
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      dfd90510
    • Nicolai Stange's avatar
      lib/mpi: purge mpi_set_buffer() · 4bdf1cfc
      Nicolai Stange authored
      mpi_set_buffer() has no in-tree users and similar functionality is provided
      by mpi_read_raw_data().
      
      Remove mpi_set_buffer().
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      4bdf1cfc
  5. 05 Apr, 2016 14 commits
    • Nicolai Stange's avatar
      lib/mpi: mpi_read_raw_from_sgl(): fix out-of-bounds buffer access · 0bb5c9ea
      Nicolai Stange authored
      Within the copying loop in mpi_read_raw_from_sgl(), the last input SGE's
      byte count gets artificially extended as follows:
      
        if (sg_is_last(sg) && (len % BYTES_PER_MPI_LIMB))
          len += BYTES_PER_MPI_LIMB - (len % BYTES_PER_MPI_LIMB);
      
      Within the following byte copying loop, this causes reads beyond that
      SGE's allocated buffer:
      
        BUG: KASAN: slab-out-of-bounds in mpi_read_raw_from_sgl+0x331/0x650
                                           at addr ffff8801e168d4d8
        Read of size 1 by task systemd-udevd/721
        [...]
        Call Trace:
         [<ffffffff818c4d35>] dump_stack+0xbc/0x117
         [<ffffffff818c4c79>] ? _atomic_dec_and_lock+0x169/0x169
         [<ffffffff814af5d1>] ? print_section+0x61/0xb0
         [<ffffffff814b1109>] print_trailer+0x179/0x2c0
         [<ffffffff814bc524>] object_err+0x34/0x40
         [<ffffffff814bfdc7>] kasan_report_error+0x307/0x8c0
         [<ffffffff814bf315>] ? kasan_unpoison_shadow+0x35/0x50
         [<ffffffff814bf38e>] ? kasan_kmalloc+0x5e/0x70
         [<ffffffff814c0ad1>] kasan_report+0x71/0xa0
         [<ffffffff81938171>] ? mpi_read_raw_from_sgl+0x331/0x650
         [<ffffffff814bf1a6>] __asan_load1+0x46/0x50
         [<ffffffff81938171>] mpi_read_raw_from_sgl+0x331/0x650
         [<ffffffff817f41b6>] rsa_verify+0x106/0x260
         [<ffffffff817f40b0>] ? rsa_set_pub_key+0xf0/0xf0
         [<ffffffff818edc79>] ? sg_init_table+0x29/0x50
         [<ffffffff817f4d22>] ? pkcs1pad_sg_set_buf+0xb2/0x2e0
         [<ffffffff817f5b74>] pkcs1pad_verify+0x1f4/0x2b0
         [<ffffffff81831057>] public_key_verify_signature+0x3a7/0x5e0
         [<ffffffff81830cb0>] ? public_key_describe+0x80/0x80
         [<ffffffff817830f0>] ? keyring_search_aux+0x150/0x150
         [<ffffffff818334a4>] ? x509_request_asymmetric_key+0x114/0x370
         [<ffffffff814b83f0>] ? kfree+0x220/0x370
         [<ffffffff818312c2>] public_key_verify_signature_2+0x32/0x50
         [<ffffffff81830b5c>] verify_signature+0x7c/0xb0
         [<ffffffff81835d0c>] pkcs7_validate_trust+0x42c/0x5f0
         [<ffffffff813c391a>] system_verify_data+0xca/0x170
         [<ffffffff813c3850>] ? top_trace_array+0x9b/0x9b
         [<ffffffff81510b29>] ? __vfs_read+0x279/0x3d0
         [<ffffffff8129372f>] mod_verify_sig+0x1ff/0x290
        [...]
      
      The exact purpose of the len extension isn't clear to me, but due to
      its form, I suspect that it's a leftover somehow accounting for leading
      zero bytes within the most significant output limb.
      
      Note however that without that len adjustement, the total number of bytes
      ever processed by the inner loop equals nbytes and thus, the last output
      limb gets written at this point. Thus the net effect of the len adjustement
      cited above is just to keep the inner loop running for some more
      iterations, namely < BYTES_PER_MPI_LIMB ones, reading some extra bytes from
      beyond the last SGE's buffer and discarding them afterwards.
      
      Fix this issue by purging the extension of len beyond the last input SGE's
      buffer length.
      
      Fixes: 2d4d1eea ("lib/mpi: Add mpi sgl helpers")
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      0bb5c9ea
    • Nicolai Stange's avatar
      lib/mpi: mpi_read_raw_from_sgl(): sanitize meaning of indices · 85d541a3
      Nicolai Stange authored
      Within the byte reading loop in mpi_read_raw_sgl(), there are two
      housekeeping indices used, z and x.
      
      At all times, the index z represents the number of output bytes covered
      by the input SGEs for which processing has completed so far. This includes
      any leading zero bytes within the most significant limb.
      
      The index x changes its meaning after the first outer loop's iteration
      though: while processing the first input SGE, it represents
      
        "number of leading zero bytes in most significant output limb" +
         "current position within current SGE"
      
      For the remaining SGEs OTOH, x corresponds just to
      
        "current position within current SGE"
      
      After all, it is only the sum of z and x that has any meaning for the
      output buffer and thus, the
      
        "number of leading zero bytes in most significant output limb"
      
      part can be moved away from x into z from the beginning, opening up the
      opportunity for cleaner code.
      
      Before the outer loop iterating over the SGEs, don't initialize z with
      zero, but with the number of leading zero bytes in the most significant
      output limb. For the inner loop iterating over a single SGE's bytes,
      get rid of the buf_shift offset to x' bounds and let x run from zero to
      sg->length - 1.
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      85d541a3
    • Nicolai Stange's avatar
      lib/mpi: mpi_read_raw_from_sgl(): fix nbits calculation · 64c09b0b
      Nicolai Stange authored
      The number of bits, nbits, is calculated in mpi_read_raw_from_sgl() as
      follows:
      
        nbits = nbytes * 8;
      
      Afterwards, the number of leading zero bits of the first byte get
      subtracted:
      
        nbits -= count_leading_zeros(*(u8 *)(sg_virt(sgl) + lzeros));
      
      However, count_leading_zeros() takes an unsigned long and thus,
      the u8 gets promoted to an unsigned long.
      
      Thus, the above doesn't subtract the number of leading zeros in the most
      significant nonzero input byte from nbits, but the number of leading
      zeros of the most significant nonzero input byte promoted to unsigned long,
      i.e. BITS_PER_LONG - 8 too many.
      
      Fix this by subtracting
      
        count_leading_zeros(...) - (BITS_PER_LONG - 8)
      
      from nbits only.
      
      Fixes: 2d4d1eea ("lib/mpi: Add mpi sgl helpers")
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      64c09b0b
    • Nicolai Stange's avatar
      lib/mpi: mpi_read_raw_from_sgl(): purge redundant clearing of nbits · 60e1b74c
      Nicolai Stange authored
      In mpi_read_raw_from_sgl(), unsigned nbits is calculated as follows:
      
        nbits = nbytes * 8;
      
      and redundantly cleared later on if nbytes == 0:
      
        if (nbytes > 0)
          ...
        else
          nbits = 0;
      
      Purge this redundant clearing for the sake of clarity.
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      60e1b74c
    • Nicolai Stange's avatar
      lib/mpi: mpi_read_raw_from_sgl(): don't include leading zero SGEs in nbytes · ab1e912e
      Nicolai Stange authored
      At the very beginning of mpi_read_raw_from_sgl(), the leading zeros of
      the input scatterlist are counted:
      
        lzeros = 0;
        for_each_sg(sgl, sg, ents, i) {
          ...
          if (/* sg contains nonzero bytes */)
            break;
      
          /* sg contains nothing but zeros here */
          ents--;
          lzeros = 0;
        }
      
      Later on, the total number of trailing nonzero bytes is calculated by
      subtracting the number of leading zero bytes from the total number of input
      bytes:
      
        nbytes -= lzeros;
      
      However, since lzeros gets reset to zero for each completely zero leading
      sg in the loop above, it doesn't include those.
      
      Besides wasting resources by allocating a too large output buffer,
      this mistake propagates into the calculation of x, the number of
      leading zeros within the most significant output limb:
      
        x = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
      
      What's more, the low order bytes of the output, equal in number to the
      extra bytes in nbytes, are left uninitialized.
      
      Fix this by adjusting nbytes for each completely zero leading scatterlist
      entry.
      
      Fixes: 2d4d1eea ("lib/mpi: Add mpi sgl helpers")
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      ab1e912e
    • Nicolai Stange's avatar
      lib/mpi: mpi_read_raw_from_sgl(): replace len argument by nbytes · b6985389
      Nicolai Stange authored
      Currently, the nbytes local variable is calculated from the len argument
      as follows:
      
        ... mpi_read_raw_from_sgl(..., unsigned int len)
        {
          unsigned nbytes;
          ...
          if (!ents)
            nbytes = 0;
          else
            nbytes = len - lzeros;
          ...
        }
      
      Given that nbytes is derived from len in a trivial way and that the len
      argument is shadowed by a local len variable in several loops, this is just
      confusing.
      
      Rename the len argument to nbytes and get rid of the nbytes local variable.
      Do the nbytes calculation in place.
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      b6985389
    • Nicolai Stange's avatar
      lib/mpi: mpi_read_buffer(): fix buffer overflow · 462696fd
      Nicolai Stange authored
      Currently, mpi_read_buffer() writes full limbs to the output buffer
      and moves memory around to purge leading zero limbs afterwards.
      
      However, with
      
        commit 9cbe21d8 ("lib/mpi: only require buffers as big as needed for
                              the integer")
      
      the caller is only required to provide a buffer large enough to hold the
      result without the leading zeros.
      
      This might result in a buffer overflow for small MP numbers with leading
      zeros.
      
      Fix this by coping the result to its final destination within the output
      buffer and not copying the leading zeros at all.
      
      Fixes: 9cbe21d8 ("lib/mpi: only require buffers as big as needed for
                            the integer")
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      462696fd
    • Nicolai Stange's avatar
      lib/mpi: mpi_read_buffer(): replace open coded endian conversion · 90f864e2
      Nicolai Stange authored
      Currently, the endian conversion from CPU order to BE is open coded in
      mpi_read_buffer().
      
      Replace this by the centrally provided cpu_to_be*() macros.
      Copy from the temporary storage on stack to the destination buffer
      by means of memcpy().
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      90f864e2
    • Nicolai Stange's avatar
      lib/mpi: mpi_read_buffer(): optimize skipping of leading zero limbs · f00fa241
      Nicolai Stange authored
      Currently, if the number of leading zeros is greater than fits into a
      complete limb, mpi_read_buffer() skips them by iterating over them
      limb-wise.
      
      Instead of skipping the high order zero limbs within the loop as shown
      above, adjust the copying loop's bounds.
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      f00fa241
    • Nicolai Stange's avatar
      lib/mpi: mpi_write_sgl(): replace open coded endian conversion · d7552906
      Nicolai Stange authored
      Currently, the endian conversion from CPU order to BE is open coded in
      mpi_write_sgl().
      
      Replace this by the centrally provided cpu_to_be*() macros.
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      d7552906
    • Nicolai Stange's avatar
      lib/mpi: mpi_write_sgl(): fix out-of-bounds stack access · cece762f
      Nicolai Stange authored
      Within the copying loop in mpi_write_sgl(), we have
      
        if (lzeros) {
          mpi_limb_t *limb1 = (void *)p - sizeof(alimb);
          mpi_limb_t *limb2 = (void *)p - sizeof(alimb)
                                     + lzeros;
          *limb1 = *limb2;
          ...
        }
      
      where p points past the end of alimb2 which lives on the stack and contains
      the current limb in BE order.
      
      The purpose of the above is to shift the non-zero bytes of alimb2 to its
      beginning in memory, i.e. to skip its leading zero bytes.
      
      However, limb2 points somewhere into the middle of alimb2 and thus, reading
      *limb2 pulls in lzero bytes from somewhere.
      
      Indeed, KASAN splats:
      
        BUG: KASAN: stack-out-of-bounds in mpi_write_to_sgl+0x4e3/0x6f0
                                            at addr ffff8800cb04f601
        Read of size 8 by task systemd-udevd/391
        page:ffffea00032c13c0 count:0 mapcount:0 mapping:   (null) index:0x0
        flags: 0x3fff8000000000()
        page dumped because: kasan: bad access detected
        CPU: 3 PID: 391 Comm: systemd-udevd Tainted: G  B  L
                                                    4.5.0-next-20160316+ #12
        [...]
        Call Trace:
         [<ffffffff8194889e>] dump_stack+0xdc/0x15e
         [<ffffffff819487c2>] ? _atomic_dec_and_lock+0xa2/0xa2
         [<ffffffff814892b5>] ? __dump_page+0x185/0x330
         [<ffffffff8150ffd6>] kasan_report_error+0x5e6/0x8b0
         [<ffffffff814724cd>] ? kzfree+0x2d/0x40
         [<ffffffff819c5bce>] ? mpi_free_limb_space+0xe/0x20
         [<ffffffff819c469e>] ? mpi_powm+0x37e/0x16f0
         [<ffffffff815109f1>] kasan_report+0x71/0xa0
         [<ffffffff819c0353>] ? mpi_write_to_sgl+0x4e3/0x6f0
         [<ffffffff8150ed34>] __asan_load8+0x64/0x70
         [<ffffffff819c0353>] mpi_write_to_sgl+0x4e3/0x6f0
         [<ffffffff819bfe70>] ? mpi_set_buffer+0x620/0x620
         [<ffffffff819c0e6f>] ? mpi_cmp+0xbf/0x180
         [<ffffffff8186e282>] rsa_verify+0x202/0x260
      
      What's more, since lzeros can be anything from 1 to sizeof(mpi_limb_t)-1,
      the above will cause unaligned accesses which is bad on non-x86 archs.
      
      Fix the issue, by preparing the starting point p for the upcoming copy
      operation instead of shifting the source memory, i.e. alimb2.
      
      Fixes: 2d4d1eea ("lib/mpi: Add mpi sgl helpers")
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      cece762f
    • Nicolai Stange's avatar
      lib/mpi: mpi_write_sgl(): purge redundant pointer arithmetic · ea122be0
      Nicolai Stange authored
      Within the copying loop in mpi_write_sgl(), we have
      
        if (lzeros) {
          ...
          p -= lzeros;
          y = lzeros;
        }
        p = p - (sizeof(alimb) - y);
      
      If lzeros == 0, then y == 0, too. Thus, lzeros gets subtracted and added
      back again to p.
      
      Purge this redundancy.
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      ea122be0
    • Nicolai Stange's avatar
      lib/mpi: mpi_write_sgl(): fix style issue with lzero decrement · 654842ef
      Nicolai Stange authored
      Within the copying loop in mpi_write_sgl(), we have
      
        if (lzeros > 0) {
          ...
          lzeros -= sizeof(alimb);
        }
      
      However, at this point, lzeros < sizeof(alimb) holds. Make this fact
      explicit by rewriting the above to
      
        if (lzeros) {
          ...
          lzeros = 0;
        }
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      654842ef
    • Nicolai Stange's avatar
      lib/mpi: mpi_write_sgl(): fix skipping of leading zero limbs · f2d1362f
      Nicolai Stange authored
      Currently, if the number of leading zeros is greater than fits into a
      complete limb, mpi_write_sgl() skips them by iterating over them limb-wise.
      
      However, it fails to adjust its internal leading zeros tracking variable,
      lzeros, accordingly: it does a
      
        p -= sizeof(alimb);
        continue;
      
      which should really have been a
      
        lzeros -= sizeof(alimb);
        continue;
      
      Since lzeros never decreases if its initial value >= sizeof(alimb), nothing
      gets copied by mpi_write_sgl() in that case.
      
      Instead of skipping the high order zero limbs within the loop as shown
      above, fix the issue by adjusting the copying loop's bounds.
      
      Fixes: 2d4d1eea ("lib/mpi: Add mpi sgl helpers")
      Signed-off-by: default avatarNicolai Stange <nicstange@gmail.com>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      f2d1362f
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