It's possible to trigger out-of-bounds read in smk_set_cipso(). For example (from root): $ echo "test 1" > /sys/fs/smackfs/cipso2 BUG: KASAN: slab-out-of-bounds in vsscanf+0x2203/0x2990 Read of size 1 at addr ffff888061b023c9 by task bash/5578

The patch adds length checks for SMK_LONG_FMT format.

The bug was found by syzkaller.

Cc: Casey Schaufler casey@schaufler-ca.com Cc: James Morris jmorris@namei.org Cc: "Serge E. Hallyn" serge@hallyn.com Cc: stable@vger.kernel.org Signed-off-by: Denis Efremov efremov@linux.com --- security/smack/smackfs.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c index e3e05c04dbd1..fad50a5a807b 100644 --- a/security/smack/smackfs.c +++ b/security/smack/smackfs.c @@ -878,6 +878,9 @@ static ssize_t smk_set_cipso(struct file *file, const char __user *buf, else rule += strlen(skp->smk_known) + 1;

+ if (rule - data + 2 * SMK_DIGITLEN - 1 >= count) + goto out; + ret = sscanf(rule, "%d", &maplevel); if (ret != 1 || maplevel > SMACK_CIPSO_MAXLEVEL) goto out; @@ -887,15 +890,19 @@ static ssize_t smk_set_cipso(struct file *file, const char __user *buf, if (ret != 1 || catlen > SMACK_CIPSO_MAXCATNUM) goto out;

- if (format == SMK_FIXED24_FMT && - count != (SMK_CIPSOMIN + catlen * SMK_DIGITLEN)) + rule += SMK_DIGITLEN; + + if ((format == SMK_FIXED24_FMT && + count != (SMK_CIPSOMIN + catlen * SMK_DIGITLEN)) || + (format == SMK_LONG_FMT && + count != (rule - data + catlen * SMK_DIGITLEN))) goto out;

memset(mapcatset, 0, sizeof(mapcatset));

for (i = 0; i < catlen; i++) { - rule += SMK_DIGITLEN; ret = sscanf(rule, "%u", &cat); + rule += SMK_DIGITLEN; if (ret != 1 || cat > SMACK_CIPSO_MAXCATNUM) goto out;