Patch "bpf: Fix hashtab overflow check on 32-bit arches" has been added to the 6.1-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    bpf: Fix hashtab overflow check on 32-bit arches

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     bpf-fix-hashtab-overflow-check-on-32-bit-arches.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 4661bdfa48f1dae0aa5b66bcdbbd7a12d23aa833
Author: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
Date:   Thu Mar 7 13:03:36 2024 +0100

    bpf: Fix hashtab overflow check on 32-bit arches
    
    [ Upstream commit 6787d916c2cf9850c97a0a3f73e08c43e7d973b1 ]
    
    The hashtab code relies on roundup_pow_of_two() to compute the number of
    hash buckets, and contains an overflow check by checking if the
    resulting value is 0. However, on 32-bit arches, the roundup code itself
    can overflow by doing a 32-bit left-shift of an unsigned long value,
    which is undefined behaviour, so it is not guaranteed to truncate
    neatly. This was triggered by syzbot on the DEVMAP_HASH type, which
    contains the same check, copied from the hashtab code. So apply the same
    fix to hashtab, by moving the overflow check to before the roundup.
    
    Fixes: daaf427c6ab3 ("bpf: fix arraymap NULL deref and missing overflow and zero size checks")
    Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
    Message-ID: <20240307120340.99577-3-toke@xxxxxxxxxx>
    Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 88c71de0a0a95..0c74cc9012d5c 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -495,7 +495,13 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 							  num_possible_cpus());
 	}
 
-	/* hash table size must be power of 2 */
+	/* hash table size must be power of 2; roundup_pow_of_two() can overflow
+	 * into UB on 32-bit arches, so check that first
+	 */
+	err = -E2BIG;
+	if (htab->map.max_entries > 1UL << 31)
+		goto free_htab;
+
 	htab->n_buckets = roundup_pow_of_two(htab->map.max_entries);
 
 	htab->elem_size = sizeof(struct htab_elem) +
@@ -505,10 +511,8 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 	else
 		htab->elem_size += round_up(htab->map.value_size, 8);
 
-	err = -E2BIG;
-	/* prevent zero size kmalloc and check for u32 overflow */
-	if (htab->n_buckets == 0 ||
-	    htab->n_buckets > U32_MAX / sizeof(struct bucket))
+	/* check for u32 overflow */
+	if (htab->n_buckets > U32_MAX / sizeof(struct bucket))
 		goto free_htab;
 
 	err = -ENOMEM;