This is a note to let you know that I've just added the patch titled
bpf: Fix stackmap overflow check on 32-bit arches
to the 6.6-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-stackmap-overflow-check-on-32-bit-arches.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit de57c382c6ba01096d94abfe636c7c5fdb970e3e
Author: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
Date: Thu Mar 7 13:03:37 2024 +0100
bpf: Fix stackmap overflow check on 32-bit arches
[ Upstream commit 7a4b21250bf79eef26543d35bd390448646c536b ]
The stackmap 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.
The commit in the fixes tag actually attempted to fix this, but the fix
did not account for the UB, so the fix only works on CPUs where an
overflow does result in a neat truncation to zero, which is not
guaranteed. Checking the value before rounding does not have this
problem.
Fixes: 6183f4d3a0a2 ("bpf: Check for integer overflow when using roundup_pow_of_two()")
Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
Reviewed-by: Bui Quang Minh <minhquangbui99@xxxxxxxxx>
Message-ID: <20240307120340.99577-4-toke@xxxxxxxxxx>
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 36775c4bc33fb..a330f38ae7335 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -91,11 +91,14 @@ static struct bpf_map *stack_map_alloc(union bpf_attr *attr)
} else if (value_size / 8 > sysctl_perf_event_max_stack)
return ERR_PTR(-EINVAL);
- /* hash table size must be power of 2 */
- n_buckets = roundup_pow_of_two(attr->max_entries);
- if (!n_buckets)
+ /* hash table size must be power of 2; roundup_pow_of_two() can overflow
+ * into UB on 32-bit arches, so check that first
+ */
+ if (attr->max_entries > 1UL << 31)
return ERR_PTR(-E2BIG);
+ n_buckets = roundup_pow_of_two(attr->max_entries);
+
cost = n_buckets * sizeof(struct stack_map_bucket *) + sizeof(*smap);
smap = bpf_map_area_alloc(cost, bpf_map_attr_numa_node(attr));
if (!smap)
