[PATCH v2 2/6] smb/client: validate new EOF for zero range

[Huiwen He <huiwen.he@linux.dev>]

From: Huiwen He <hehuiwen@kylinos.cn>

When FALLOC_FL_ZERO_RANGE is used without FALLOC_FL_KEEP_SIZE,
smb3_zero_range() may extend EOF without checking RLIMIT_FSIZE, allowing
the file to grow beyond the caller's file-size limit.

Fix this by calling inode_newsize_ok() before sending the zero-range
request when the operation would extend EOF.

Reproducer, using a file on a CIFS mount:

	bash -c '
	        FILE=/mnt/cifs/repro

	        trap "" SIGXFSZ
	        ulimit -f 3072

	        truncate -s 2M "$FILE"
	        fallocate --zero-range -o 0 -l 4M "$FILE"
	        echo "fallocate rc=$?"
	        stat -c "file size=%s" "$FILE"
	'

Before this change, the operation succeeds despite the 3 MiB limit:

	fallocate rc=0
	file size=4194304

After this change, fallocate fails and leaves the file at 2 MiB.

Fixes: 72c419d9b073 ("cifs: fix smb3_zero_range so it can expand the file-size when required")
Signed-off-by: Huiwen He <hehuiwen@kylinos.cn>
Reviewed-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
---
 fs/smb/client/smb2ops.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c
index bc7dda6d825a..f823f9bc90eb 100644
--- a/fs/smb/client/smb2ops.c
+++ b/fs/smb/client/smb2ops.c
@@ -3442,6 +3442,13 @@ static long smb3_zero_range(struct file *file, struct cifs_tcon *tcon,
 	trace_smb3_zero_enter(xid, cfile->fid.persistent_fid, tcon->tid,
 			      ses->Suid, offset, len);
 
+	new_size = offset + len;
+	if (!keep_size && i_size_read(inode) < new_size) {
+		rc = inode_newsize_ok(inode, new_size);
+		if (rc)
+			goto out;
+	}
+
 	filemap_invalidate_lock(inode->i_mapping);
 
 	netfs_read_sizes(inode, &i_size, &remote_i_size, &zero_point);
@@ -3472,7 +3479,6 @@ static long smb3_zero_range(struct file *file, struct cifs_tcon *tcon,
 	/*
 	 * do we also need to change the size of the file?
 	 */
-	new_size = offset + len;
 	if (keep_size == false && (unsigned long long)i_size_read(inode) < new_size) {
 		rc = SMB2_set_eof(xid, tcon, cfile->fid.persistent_fid,
 				  cfile->fid.volatile_fid, cfile->pid, new_size);
@@ -3489,6 +3495,7 @@ static long smb3_zero_range(struct file *file, struct cifs_tcon *tcon,
 
  zero_range_exit:
 	filemap_invalidate_unlock(inode->i_mapping);
+ out:
 	free_xid(xid);
 	if (rc)
 		trace_smb3_zero_err(xid, cfile->fid.persistent_fid, tcon->tid,
-- 
2.43.0