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Nicolai Stange 0bb5c9ead6 lib/mpi: mpi_read_raw_from_sgl(): fix out-of-bounds buffer access 
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: 2d4d1eea54 ("lib/mpi: Add mpi sgl helpers")
Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
 		2016-04-05 20:35:51 +08:00
..
Makefile MPILIB: Reinstate mpi_cmp[_ui]() and export for RSA signature verification 2012-10-08 13:50:15 +10:30
generic_mpih-add1.c crypto: GnuPG based MPI lib - source files (part 1) 2011-11-09 11:45:22 +02:00
generic_mpih-lshift.c crypto: GnuPG based MPI lib - source files (part 1) 2011-11-09 11:45:22 +02:00
generic_mpih-mul1.c crypto: GnuPG based MPI lib - source files (part 1) 2011-11-09 11:45:22 +02:00
generic_mpih-mul2.c crypto: GnuPG based MPI lib - source files (part 1) 2011-11-09 11:45:22 +02:00
generic_mpih-mul3.c crypto: GnuPG based MPI lib - source files (part 1) 2011-11-09 11:45:22 +02:00
generic_mpih-rshift.c crypto: GnuPG based MPI lib - source files (part 1) 2011-11-09 11:45:22 +02:00
generic_mpih-sub1.c crypto: GnuPG based MPI lib - source files (part 1) 2011-11-09 11:45:22 +02:00
longlong.h lib/mpi: avoid assembler warning 2016-02-28 03:26:34 +08:00
mpi-bit.c MPILIB: Provide count_leading/trailing_zeros() based on arch functions 2012-10-08 13:50:11 +10:30
mpi-cmp.c MPILIB: Fix comparison of negative MPIs 2015-01-14 16:10:12 +00:00
mpi-inline.h lib/mpi: use "static inline" instead of "extern inline" 2016-02-28 03:26:34 +08:00
mpi-internal.h lib/mpi: use "static inline" instead of "extern inline" 2016-02-28 03:26:34 +08:00
mpi-pow.c MPILIB: Provide count_leading/trailing_zeros() based on arch functions 2012-10-08 13:50:11 +10:30
mpicoder.c lib/mpi: mpi_read_raw_from_sgl(): fix out-of-bounds buffer access 2016-04-05 20:35:51 +08:00
mpih-cmp.c crypto: GnuPG based MPI lib - source files (part 1) 2011-11-09 11:45:22 +02:00
mpih-div.c Remove unused code from MPI library 2012-05-26 11:51:03 +10:00
mpih-mul.c Remove unused code from MPI library 2012-05-26 11:51:03 +10:00
mpiutil.c MPILIB: add mpi_read_buf() and mpi_get_size() helpers 2015-06-16 14:35:06 +08:00