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| author | Hannes Frederic Sowa <hannes@stressinduktion.org> | 2014-07-19 01:26:41 +0400 |
|---|---|---|
| committer | Theodore Ts'o <tytso@mit.edu> | 2014-07-19 09:42:13 +0400 |
| commit | 79a8468747c5f95ed3d5ce8376a3e82e0c5857fc (patch) | |
| tree | c84aca1e2222c1966b62bd87f9b702f7782b8f9c /drivers/char | |
| parent | 1795cd9b3a91d4b5473c97f491d63892442212ab (diff) | |
| download | linux-79a8468747c5f95ed3d5ce8376a3e82e0c5857fc.tar.xz | |
random: check for increase of entropy_count because of signed conversion
The expression entropy_count -= ibytes << (ENTROPY_SHIFT + 3) could
actually increase entropy_count if during assignment of the unsigned
expression on the RHS (mind the -=) we reduce the value modulo
2^width(int) and assign it to entropy_count. Trinity found this.
[ Commit modified by tytso to add an additional safety check for a
negative entropy_count -- which should never happen, and to also add
an additional paranoia check to prevent overly large count values to
be passed into urandom_read(). ]
Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
Diffstat (limited to 'drivers/char')
| -rw-r--r-- | drivers/char/random.c | 17 |
1 files changed, 14 insertions, 3 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c index 0a7ac0a7b252..71529e196b84 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -641,7 +641,7 @@ retry: } while (unlikely(entropy_count < pool_size-2 && pnfrac)); } - if (entropy_count < 0) { + if (unlikely(entropy_count < 0)) { pr_warn("random: negative entropy/overflow: pool %s count %d\n", r->name, entropy_count); WARN_ON(1); @@ -981,7 +981,7 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min, int reserved) { int entropy_count, orig; - size_t ibytes; + size_t ibytes, nfrac; BUG_ON(r->entropy_count > r->poolinfo->poolfracbits); @@ -999,7 +999,17 @@ retry: } if (ibytes < min) ibytes = 0; - if ((entropy_count -= ibytes << (ENTROPY_SHIFT + 3)) < 0) + + if (unlikely(entropy_count < 0)) { + pr_warn("random: negative entropy count: pool %s count %d\n", + r->name, entropy_count); + WARN_ON(1); + entropy_count = 0; + } + nfrac = ibytes << (ENTROPY_SHIFT + 3); + if ((size_t) entropy_count > nfrac) + entropy_count -= nfrac; + else entropy_count = 0; if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig) @@ -1376,6 +1386,7 @@ urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) "with %d bits of entropy available\n", current->comm, nonblocking_pool.entropy_total); + nbytes = min_t(size_t, nbytes, INT_MAX >> (ENTROPY_SHIFT + 3)); ret = extract_entropy_user(&nonblocking_pool, buf, nbytes); trace_urandom_read(8 * nbytes, ENTROPY_BITS(&nonblocking_pool), |