audit: fix out-of-bounds read in audit_compare_dname_path()

When a watch on dir=/ is combined with an fsnotify event for a
single-character name directly under / (e.g., creating /a), an
out-of-bounds read can occur in audit_compare_dname_path().

The helper parent_len() returns 1 for "/". In audit_compare_dname_path(),
when parentlen equals the full path length (1), the code sets p = path + 1
and pathlen = 1 - 1 = 0. The subsequent loop then dereferences
p[pathlen - 1] (i.e., p[-1]), causing an out-of-bounds read.

Fix this by adding a pathlen > 0 check to the while loop condition
to prevent the out-of-bounds access.

Cc: stable@vger.kernel.org
Fixes: e92eebb0d611 ("audit: fix suffixed '/' filename matching")
Reported-by: Stanislav Fort <disclosure@aisle.com>
Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
Signed-off-by: Stanislav Fort <stanislav.fort@aisle.com>
[PM: subject tweak, sign-off email fixes]
Signed-off-by: Paul Moore <paul@paul-moore.com>

diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
index e3f42018ed46fa7cc31d5aeb9b5a3b11a9c03cae..f7708fe2c4572237fad94ea6a3320b661decf156 100644 (file)
--- a/kernel/auditfilter.c
+++ b/kernel/auditfilter.c
@@ -1326,7 +1326,7 @@ int audit_compare_dname_path(const struct qstr *dname, const char *path, int par
 
        /* handle trailing slashes */
        pathlen -= parentlen;
-       while (p[pathlen - 1] == '/')
+       while (pathlen > 0 && p[pathlen - 1] == '/')
                pathlen--;
 
        if (pathlen != dlen)