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ksmbd: fix null pointer dereference in proc_show_files()

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When a SMB2 client opens a file with a durable v2 handle and then issues
SMB2 SESSION_LOGOFF, session_fd_check() clears fp->tcon = NULL on the
reconnectable file pointer but leaves the fp registered in global_ft.idr
until the durable scavenger fires (up to fp->durable_timeout seconds
later).

During that window any read of /proc/fs/ksmbd/files (mode 0400) panics
the kernel because proc_show_files() walks global_ft.idr and
unconditionally dereferences fp->tcon->id with no NULL guard.

Reproducer requires only a successful SMB2 SESSION_SETUP and a share
configured with 'durable handles = yes'. KASAN report on mainline
70390501d194:

  general protection fault, probably for non-canonical address
  0xdffffc0000000000: 0000 [#1] SMP KASAN PTI
  KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
  RIP: 0010:proc_show_files+0x118/0x740
  Call Trace:
   proc_show_files+0x118/0x740
   seq_read_iter+0x4ef/0xe10
   proc_reg_read_iter+0x1b7/0x280
   ...

Guard the dereference. A durable-disconnected fp legitimately has no
tcon; report its tree id as 0 rather than oopsing.

Fixes: b38f99c121 ("ksmbd: add procfs interface for runtime monitoring and statistics")
Cc: stable@vger.kernel.org
Signed-off-by: Jeremy Laratro <research@aradex.io>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
This commit is contained in:
Jeremy Laratro 2026-05-13 08:23:26 +09:00 committed by Steve French
parent af92ee994c
commit 904901561e
1 changed files with 1 additions and 1 deletions
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2
fs/smb/server/vfs_cache.c
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@ -81,7 +81,7 @@ static int proc_show_files(struct seq_file *m, void *v)
read_lock(&global_ft.lock);
idr_for_each_entry(global_ft.idr, fp, id) {
seq_printf(m, "%#-10x %#-10llx %#-10llx %#-10x",
fp->tcon->id,
fp->tcon ? fp->tcon->id : 0,
fp->persistent_id,
fp->volatile_id,
atomic_read(&fp->refcount));