The patch below does not apply to the 5.4-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-5.4.y git checkout FETCH_HEAD git cherry-pick -x dff4f9ff5d7f289e4545cc936362e01ed3252742 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025101644-legacy-starch-6a67@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From dff4f9ff5d7f289e4545cc936362e01ed3252742 Mon Sep 17 00:00:00 2001 From: Anderson Nascimento anderson@allelesecurity.com Date: Mon, 8 Sep 2025 09:49:02 -0300 Subject: [PATCH] btrfs: avoid potential out-of-bounds in btrfs_encode_fh()
The function btrfs_encode_fh() does not properly account for the three cases it handles.
Before writing to the file handle (fh), the function only returns to the user BTRFS_FID_SIZE_NON_CONNECTABLE (5 dwords, 20 bytes) or BTRFS_FID_SIZE_CONNECTABLE (8 dwords, 32 bytes).
However, when a parent exists and the root ID of the parent and the inode are different, the function writes BTRFS_FID_SIZE_CONNECTABLE_ROOT (10 dwords, 40 bytes).
If *max_len is not large enough, this write goes out of bounds because BTRFS_FID_SIZE_CONNECTABLE_ROOT is greater than BTRFS_FID_SIZE_CONNECTABLE originally returned.
This results in an 8-byte out-of-bounds write at fid->parent_root_objectid = parent_root_id.
A previous attempt to fix this issue was made but was lost.
https://lore.kernel.org/all/4CADAEEC020000780001B32C@vpn.id2.novell.com/
Although this issue does not seem to be easily triggerable, it is a potential memory corruption bug that should be fixed. This patch resolves the issue by ensuring the function returns the appropriate size for all three cases and validates that *max_len is large enough before writing any data.
Fixes: be6e8dc0ba84 ("NFS support for btrfs - v3") CC: stable@vger.kernel.org # 3.0+ Signed-off-by: Anderson Nascimento anderson@allelesecurity.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com
diff --git a/fs/btrfs/export.c b/fs/btrfs/export.c index d062ac521051..230d9326b685 100644 --- a/fs/btrfs/export.c +++ b/fs/btrfs/export.c @@ -23,7 +23,11 @@ static int btrfs_encode_fh(struct inode *inode, u32 *fh, int *max_len, int type;
if (parent && (len < BTRFS_FID_SIZE_CONNECTABLE)) { - *max_len = BTRFS_FID_SIZE_CONNECTABLE; + if (btrfs_root_id(BTRFS_I(inode)->root) != + btrfs_root_id(BTRFS_I(parent)->root)) + *max_len = BTRFS_FID_SIZE_CONNECTABLE_ROOT; + else + *max_len = BTRFS_FID_SIZE_CONNECTABLE; return FILEID_INVALID; } else if (len < BTRFS_FID_SIZE_NON_CONNECTABLE) { *max_len = BTRFS_FID_SIZE_NON_CONNECTABLE; @@ -45,6 +49,8 @@ static int btrfs_encode_fh(struct inode *inode, u32 *fh, int *max_len, parent_root_id = btrfs_root_id(BTRFS_I(parent)->root);
if (parent_root_id != fid->root_objectid) { + if (*max_len < BTRFS_FID_SIZE_CONNECTABLE_ROOT) + return FILEID_INVALID; fid->parent_root_objectid = parent_root_id; len = BTRFS_FID_SIZE_CONNECTABLE_ROOT; type = FILEID_BTRFS_WITH_PARENT_ROOT;