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 <[email protected]>
Cc: James Morris <[email protected]>
Cc: "Serge E. Hallyn" <[email protected]>
Cc: <[email protected]>
Signed-off-by: Denis Efremov <[email protected]>
---
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;
--
2.21.0