[PATCH v2] audit: fix potential integer overflow in audit_log_n_hex()

[Ricardo Robaina]

The function calculates new_len as len << 1 for hex encoding. This
has two overflow risks: the shift itself can overflow when len is
large, and the result can be truncated when assigned to new_len
(declared as int) from the size_t calculation.

Fix by using check_shl_overflow() to catch shift overflow and
changing new_len and loop counter i to size_t to prevent truncation.

Fixes: 168b7173959f ("AUDIT: Clean up logging of untrusted strings")
Signed-off-by: Ricardo Robaina <rroba...@redhat.com>
---
Changes in v2:
- Use check_shl_overflow() instead of manual overflow check.

 kernel/audit.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/audit.c b/kernel/audit.c
index e1d489bc2dff..8ca268610641 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -62,6 +62,7 @@
 #include <net/ip.h>
 #include <net/ipv6.h>
 #include <linux/sctp.h>
+#include <linux/overflow.h>
 
 #include "audit.h"
 
@@ -2076,7 +2077,8 @@ void audit_log_format(struct audit_buffer *ab, const char 
*fmt, ...)
 void audit_log_n_hex(struct audit_buffer *ab, const unsigned char *buf,
                size_t len)
 {
-       int i, avail, new_len;
+       int avail;
+       size_t i, new_len;
        unsigned char *ptr;
        struct sk_buff *skb;
 
@@ -2084,9 +2086,13 @@ void audit_log_n_hex(struct audit_buffer *ab, const 
unsigned char *buf,
                return;
 
        BUG_ON(!ab->skb);
+
        skb = ab->skb;
        avail = skb_tailroom(skb);
-       new_len = len<<1;
+
+       if (check_shl_overflow(len, 1, &new_len))
+               return;
+
        if (new_len >= avail) {
                /* Round the buffer request up to the next multiple */
                new_len = AUDIT_BUFSIZ*(((new_len-avail)/AUDIT_BUFSIZ) + 1);
-- 
2.53.0