In the Linux kernel, the following vulnerability has been resolved: smb/client: validate new EOF for insert range smb3_insert_range() does

In the Linux kernel, the following vulnerability has been resolved:

smb/client: validate new EOF for insert range

smb3_insert_range() does not check if the new file size
(i_size + len) is valid. This allows FALLOC_FL_INSERT_RANGE to bypass
RLIMIT_FSIZE, exceed s_maxbytes, or produce a size outside the loff_t
range.

Use check_add_overflow() to calculate the new EOF. Validate it with
inode_newsize_ok() before modifying the file.

Reproducer, using a file on a CIFS mount:

 1bash -c '
 2	FILE=/mnt/cifs/repro
 3 
 4	trap "" SIGXFSZ
 5	ulimit -f 3072		# RLIMIT_FSIZE = 3 MiB
 6 
 7	# A regular write is stopped at 3 MiB.
 8	dd if=/dev/zero of="$FILE" bs=1M count=4 status=none
 9	stat -c "size after write: %s" "$FILE"
10 
11	# Insert 2 MiB into a 2 MiB file.
12	truncate -s 2M "$FILE"
13	fallocate -i -o 0 -l 2M "$FILE"
14	stat -c "size after insert: %s" "$FILE"
15'

Before this change, the regular write stops at the 3 MiB limit, but
insert range grows the file to 4 MiB:

 1dd: error writing '/mnt/cifs/repro': File too large
 2size after write: 3145728
 3size after insert: 4194304

After this change, insert range also fails at the limit and leaves the
2 MiB file unchanged:

 1dd: error writing '/mnt/cifs/repro': File too large
 2size after write: 3145728
 3fallocate: fallocate failed: File too large
 4size after insert: 2097152