Patch "bpf: Protect against int overflow for stack access size" has been added to the 5.15-stable tree

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

    bpf: Protect against int overflow for stack access size

to the 5.15-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-protect-against-int-overflow-for-stack-access-si.patch
and it can be found in the queue-5.15 subdirectory.

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



commit d781f623f9a670fff938b70c55bd9d0478b92912
Author: Andrei Matei <andreimatei1@xxxxxxxxx>
Date:   Tue Mar 26 22:42:45 2024 -0400

    bpf: Protect against int overflow for stack access size
    
    [ 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@xxxxxxxxxxxxxxxxxxxxxxxxx
    Reported-by: syzbot+aafd0513053a1cbf52ef@xxxxxxxxxxxxxxxxxxxxxxxxx
    Closes: https://lore.kernel.org/bpf/CAADnVQLORV5PT0iTAhRER+iLBTkByCYNBYyvBSgjN1T31K+gOw@xxxxxxxxxxxxxx/
    Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
    Signed-off-by: Andrei Matei <andreimatei1@xxxxxxxxx>
    Link: https://lore.kernel.org/r/20240327024245.318299-3-andreimatei1@xxxxxxxxx
    Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f099c5481b662..008ddb694c8a1 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4320,6 +4320,11 @@ static int check_stack_access_within_bounds(
 	err = check_stack_slot_within_bounds(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)) {




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