FAILED: patch "[PATCH] ksmbd: fix out-of-bounds write in smb2_get_ea() EA alignment" failed to apply to 5.15-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.15-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 <stable@vger.kernel.org>.

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-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 30010c952077a1c89ecdd71fc4d574c75a8f5617
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026042445-graduate-unvaried-2a31@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

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

From 30010c952077a1c89ecdd71fc4d574c75a8f5617 Mon Sep 17 00:00:00 2001
From: Tristan Madani <tristan@talencesecurity.com>
Date: Fri, 17 Apr 2026 19:33:17 +0000
Subject: [PATCH] ksmbd: fix out-of-bounds write in smb2_get_ea() EA alignment

smb2_get_ea() applies 4-byte alignment padding via memset() after
writing each EA entry. The bounds check on buf_free_len is performed
before the value memcpy, but the alignment memset fires unconditionally
afterward with no check on remaining space.

When the EA value exactly fills the remaining buffer (buf_free_len == 0
after value subtraction), the alignment memset writes 1-3 NUL bytes
past the buf_free_len boundary. In compound requests where the response
buffer is shared across commands, the first command (e.g., READ) can
consume most of the buffer, leaving a tight remainder for the QUERY_INFO
EA response. The alignment memset then overwrites past the physical
kvmalloc allocation into adjacent kernel heap memory.

Add a bounds check before the alignment memset to ensure buf_free_len
can accommodate the padding bytes.

This is the same bug pattern fixed by commit beef2634f81f ("ksmbd: fix
potencial OOB in get_file_all_info() for compound requests") and
commit fda9522ed6af ("ksmbd: fix OOB write in QUERY_INFO for compound
requests"), both of which added bounds checks before unconditional
writes in QUERY_INFO response handlers.

Cc: stable@vger.kernel.org
Fixes: e2b76ab8b5c9 ("ksmbd: add support for read compound")
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 395007c82831..652b6771ccaf 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -4818,6 +4818,8 @@ static int smb2_get_ea(struct ksmbd_work *work, struct ksmbd_file *fp,
 		/* align next xattr entry at 4 byte bundary */
 		alignment_bytes = ((next_offset + 3) & ~3) - next_offset;
 		if (alignment_bytes) {
+			if (buf_free_len < alignment_bytes)
+				break;
 			memset(ptr, '\0', alignment_bytes);
 			ptr += alignment_bytes;
 			next_offset += alignment_bytes;