6.6-stable review patch. If anyone has any objections, please let me know.
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From: Andrei Matei andreimatei1@gmail.com
[ Upstream commit ecc6a2101840177e57c925c102d2d29f260d37c8 ]
This patch re-introduces protection against the size of access to stack memory being negative; the access size can appear negative as a result of overflowing its signed int representation. This should not actually happen, as there are other protections along the way, but we should protect against it anyway. One code path was missing such protections (fixed in the previous patch in the series), causing out-of-bounds array accesses in check_stack_range_initialized(). This patch causes the verification of a program with such a non-sensical access size to fail.
This check used to exist in a more indirect way, but was inadvertendly removed in a833a17aeac7.
Fixes: a833a17aeac7 ("bpf: Fix verification of indirect var-off stack access") Reported-by: syzbot+33f4297b5f927648741a@syzkaller.appspotmail.com Reported-by: syzbot+aafd0513053a1cbf52ef@syzkaller.appspotmail.com Closes: https://lore.kernel.org/bpf/CAADnVQLORV5PT0iTAhRER+iLBTkByCYNBYyvBSgjN1T31K+... Acked-by: Andrii Nakryiko andrii@kernel.org Signed-off-by: Andrei Matei andreimatei1@gmail.com Link: https://lore.kernel.org/r/20240327024245.318299-3-andreimatei1@gmail.com Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/verifier.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 396c4c66932f2..c9fc734989c68 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -6637,6 +6637,11 @@ static int check_stack_access_within_bounds( err = check_stack_slot_within_bounds(env, min_off, state, type); if (!err && max_off > 0) err = -EINVAL; /* out of stack access into non-negative offsets */ + if (!err && access_size < 0) + /* access_size should not be negative (or overflow an int); others checks + * along the way should have prevented such an access. + */ + err = -EFAULT; /* invalid negative access size; integer overflow? */
if (err) { if (tnum_is_const(reg->var_off)) {