ksmbd: validate COPYCHUNK source and target ranges

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ksmbd_vfs_copy_file_ranges() rejects negative source offsets in the
copy loop, but it does not validate target offsets. It also calculates
lock and overlap endpoints before ensuring that either range fits within
MAX_LFS_FILESIZE.

When the target is an alternate data stream, the buffered path passes a
negative target offset to ksmbd_vfs_stream_write(). Let n be Length and
let -d be TargetOffset, where 0 < d < n <= XATTR_SIZE_MAX. For an empty
stream, the writer allocates n - d bytes, then copies n bytes starting d
bytes before the allocation. An authenticated SMB client can control d
and the source data, overwrite kernel heap memory, and crash the host.

Validate both ranges before lock, overlap, or I/O calculations.

Fixes: 8482150a07 ("ksmbd: support copychunk for alternate data streams")
Assisted-by: Antiproof:GPT-5.6-Sol
Signed-off-by: Alon Shakevsky <shakevsky@berkeley.edu>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

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Alon Shakevsky 2026-09-01 00:05:31 +00:00 • committed by Namjae Jeon

parent 0e75389962

commit 0480cee8cc

1 changed files with 11 additions and 1 deletions

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fs/smb/server/vfs.c

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