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ubifs: fix out-of-bounds read in signature length check

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ubifs_sb_verify_signature() bounds the on-disk ubifs_sig_node->len field
before handing the signature payload to verify_pkcs7_signature(), but the
check has the wrong sign:

	if (le32_to_cpu(signode->len) > snod->len + sizeof(struct ubifs_sig_node))

The signature bytes start sizeof(struct ubifs_sig_node) (UBIFS_SIG_NODE_SZ,
64 bytes) into the node, so the payload is at most

	snod->len - sizeof(struct ubifs_sig_node)

bytes long. Adding the header size instead of subtracting it accepts a
declared length up to 2 * UBIFS_SIG_NODE_SZ larger than the node actually
holds -- past the end of c->sbuf, which is vmalloc(c->leb_size).
verify_pkcs7_signature() -> pkcs7_parse_message() -> asn1_ber_decoder()
is then handed that inflated length and reads beyond the allocation while
walking the DER headers. The node length comes straight from the mounted
image, so a crafted signed UBIFS image reaches this via
ubifs_read_superblock() before the signature is cryptographically checked.

snod->len is guaranteed to be >= UBIFS_SIG_NODE_SZ by the node scanner
(c->ranges[UBIFS_SIG_NODE].min_len == UBIFS_SIG_NODE_SZ), so the corrected
subtraction cannot underflow. Legitimately signed images are unaffected: a
correct superblock never declares a signature longer than the node it is
embedded in.

Fixes: 817aa09484 ("ubifs: support offline signed images")
Cc: stable@vger.kernel.org
Signed-off-by: Ibrahim Hashimov <security@auditcode.ai>
Assisted-by: AuditCode-AI:2026.07
Reviewed-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
This commit is contained in:
Ibrahim Hashimov 2026-07-24 09:43:27 +02:00 committed by Richard Weinberger
parent be04fce994
commit 95d27c1708
1 changed files with 1 additions and 1 deletions
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2
fs/ubifs/auth.c
View File

@ -217,7 +217,7 @@ int ubifs_sb_verify_signature(struct ubifs_info *c,
signode = snod->node;
if (le32_to_cpu(signode->len) > snod->len + sizeof(struct ubifs_sig_node)) {
if (le32_to_cpu(signode->len) > snod->len - sizeof(struct ubifs_sig_node)) {
ubifs_err(c, "invalid signature len %d", le32_to_cpu(signode->len));
err = -EINVAL;
goto out_destroy;