FAILED: patch "[PATCH] ima: fix out-of-bounds read in xattr_verify()" failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x 5ff232d31106f45ac87c3b64e1d35a0667777797
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026081311-refutable-kiln-56fe@gregkh' --subject-prefix 'PATCH 5.10.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 5ff232d31106f45ac87c3b64e1d35a0667777797 Mon Sep 17 00:00:00 2001
From: Lincoln Wallace <[email protected]>
Date: Mon, 3 Aug 2026 10:50:21 -0300
Subject: [PATCH] ima: fix out-of-bounds read in xattr_verify()

The digest-length check in xattr_verify() mixes int and size_t:

	if (xattr_len - sizeof(xattr_value->type) - hash_start >=
			iint->ima_hash->length)

sizeof() yields size_t, so the usual arithmetic conversions promote the whole left-hand side to unsigned 64-bit before the subtraction runs. For a truncated xattr this underflows instead of going negative:
a 1-byte IMA_XATTR_DIGEST_NG xattr (xattr_len == 1, hash_start == 1) turns "1 - 1 - 1" into SIZE_MAX, which is trivially >= ima_hash->length. The check then passes and the following memcmp() reads iint->ima_hash->length bytes starting past the end of the buffer vfs_getxattr_alloc() allocated for it.

Nothing upstream clamps xattr_len back into a safe range first:
ima_get_hash_algo() only special-cases xattr_len < 2 to pick a default algorithm, and evm_verifyxattr() returns INTEGRITY_UNKNOWN rather than failing when no HMAC key is loaded, so a truncated security.ima value reaches the length check as-is.

Rewrite the comparison so every operand stays a signed int and no implicit conversion to size_t can occur.

index 18d0d9154317..ced2e131b061 100644
@@ -274,8 +274,13 @@ static int xattr_verify(enum ima_hooks func, struct ima_iint_cache *iint,
 		} else {
 			set_bit(IMA_DIGSIG, &iint->atomic_flags);
 		}
-		if (xattr_len - sizeof(xattr_value->type) - hash_start >=
-				iint->ima_hash->length)
+		/*
+		 * Use addition, not subtraction: sizeof() forces unsigned
+		 * math and a short xattr_len would wrap around, bypassing
+		 * this bounds check.
+		 */
+		if (xattr_len >= (int)sizeof(xattr_value->type) + hash_start +
+				(int)iint->ima_hash->length)
 			/*
 			 * xattr length may be longer. md5 hash in previous
 			 * version occupied 20 bytes in xattr, instead of 16

The digest-length check in xattr_verify() mixes int and size_t:

	if (xattr_len - sizeof(xattr_value->type) - hash_start >=
			iint->ima_hash->length)

sizeof() yields size_t, so the usual arithmetic conversions promote the whole left-hand side to unsigned 64-bit before the subtraction runs. For a truncated xattr this underflows instead of going negative:
a 1-byte IMA_XATTR_DIGEST_NG xattr (xattr_len == 1, hash_start == 1) turns "1 - 1 - 1" into SIZE_MAX, which is trivially >= ima_hash->length. The check then passes and the following memcmp() reads iint->ima_hash->length bytes starting past the end of the buffer vfs_getxattr_alloc() allocated for it.

Nothing upstream clamps xattr_len back into a safe range first:
ima_get_hash_algo() only special-cases xattr_len < 2 to pick a default algorithm, and evm_verifyxattr() returns INTEGRITY_UNKNOWN rather than failing when no HMAC key is loaded, so a truncated security.ima value reaches the length check as-is.

Rewrite the comparison so every operand stays a signed int and no implicit conversion to size_t can occur.

---
Context conflict only: the IMA_XATTR_DIGEST case was restructured after 5.10 by commit 7aa5783d9564 ("ima: Allow imasig requirement to be satisfied by EVM portable signatures"). The fix itself is identical to upstream.

 security/integrity/ima/ima_appraise.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

index 7122a359a268..615a20b9eb52 100644
@@ -242,8 +242,13 @@ static int xattr_verify(enum ima_hooks func, struct integrity_iint_cache *iint,
 			break;
 		}
 		clear_bit(IMA_DIGSIG, &iint->atomic_flags);
-		if (xattr_len - sizeof(xattr_value->type) - hash_start >=
-				iint->ima_hash->length)
+		/*
+		 * Use addition, not subtraction: sizeof() forces unsigned
+		 * math and a short xattr_len would wrap around, bypassing
+		 * this bounds check.
+		 */
+		if (xattr_len >= (int)sizeof(xattr_value->type) + hash_start +
+				(int)iint->ima_hash->length)
 			/*
 			 * xattr length may be longer. md5 hash in previous
 			 * version occupied 20 bytes in xattr, instead of 16

2.53.0

Queued for 5.10, thanks.

Thanks,
Sasha