Patch "nfs: fix panic when nfs4_ff_layout_prepare_ds() fails" has been added to the 6.1-stable tree

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This is a note to let you know that I've just added the patch titled

    nfs: fix panic when nfs4_ff_layout_prepare_ds() fails

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     nfs-fix-panic-when-nfs4_ff_layout_prepare_ds-fails.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit fc0e450faa15b2731573c77e888ebc505cffce4a
Author: Josef Bacik <josef@xxxxxxxxxxxxxx>
Date:   Mon Mar 11 11:11:53 2024 -0400

    nfs: fix panic when nfs4_ff_layout_prepare_ds() fails
    
    [ Upstream commit 719fcafe07c12646691bd62d7f8d94d657fa0766 ]
    
    We've been seeing the following panic in production
    
    BUG: kernel NULL pointer dereference, address: 0000000000000065
    PGD 2f485f067 P4D 2f485f067 PUD 2cc5d8067 PMD 0
    RIP: 0010:ff_layout_cancel_io+0x3a/0x90 [nfs_layout_flexfiles]
    Call Trace:
     <TASK>
     ? __die+0x78/0xc0
     ? page_fault_oops+0x286/0x380
     ? __rpc_execute+0x2c3/0x470 [sunrpc]
     ? rpc_new_task+0x42/0x1c0 [sunrpc]
     ? exc_page_fault+0x5d/0x110
     ? asm_exc_page_fault+0x22/0x30
     ? ff_layout_free_layoutreturn+0x110/0x110 [nfs_layout_flexfiles]
     ? ff_layout_cancel_io+0x3a/0x90 [nfs_layout_flexfiles]
     ? ff_layout_cancel_io+0x6f/0x90 [nfs_layout_flexfiles]
     pnfs_mark_matching_lsegs_return+0x1b0/0x360 [nfsv4]
     pnfs_error_mark_layout_for_return+0x9e/0x110 [nfsv4]
     ? ff_layout_send_layouterror+0x50/0x160 [nfs_layout_flexfiles]
     nfs4_ff_layout_prepare_ds+0x11f/0x290 [nfs_layout_flexfiles]
     ff_layout_pg_init_write+0xf0/0x1f0 [nfs_layout_flexfiles]
     __nfs_pageio_add_request+0x154/0x6c0 [nfs]
     nfs_pageio_add_request+0x26b/0x380 [nfs]
     nfs_do_writepage+0x111/0x1e0 [nfs]
     nfs_writepages_callback+0xf/0x30 [nfs]
     write_cache_pages+0x17f/0x380
     ? nfs_pageio_init_write+0x50/0x50 [nfs]
     ? nfs_writepages+0x6d/0x210 [nfs]
     ? nfs_writepages+0x6d/0x210 [nfs]
     nfs_writepages+0x125/0x210 [nfs]
     do_writepages+0x67/0x220
     ? generic_perform_write+0x14b/0x210
     filemap_fdatawrite_wbc+0x5b/0x80
     file_write_and_wait_range+0x6d/0xc0
     nfs_file_fsync+0x81/0x170 [nfs]
     ? nfs_file_mmap+0x60/0x60 [nfs]
     __x64_sys_fsync+0x53/0x90
     do_syscall_64+0x3d/0x90
     entry_SYSCALL_64_after_hwframe+0x46/0xb0
    
    Inspecting the core with drgn I was able to pull this
    
      >>> prog.crashed_thread().stack_trace()[0]
      #0 at 0xffffffffa079657a (ff_layout_cancel_io+0x3a/0x84) in ff_layout_cancel_io at fs/nfs/flexfilelayout/flexfilelayout.c:2021:27
      >>> prog.crashed_thread().stack_trace()[0]['idx']
      (u32)1
      >>> prog.crashed_thread().stack_trace()[0]['flseg'].mirror_array[1].mirror_ds
      (struct nfs4_ff_layout_ds *)0xffffffffffffffed
    
    This is clear from the stack trace, we call nfs4_ff_layout_prepare_ds()
    which could error out initializing the mirror_ds, and then we go to
    clean it all up and our check is only for if (!mirror->mirror_ds).  This
    is inconsistent with the rest of the users of mirror_ds, which have
    
      if (IS_ERR_OR_NULL(mirror_ds))
    
    to keep from tripping over this exact scenario.  Fix this up in
    ff_layout_cancel_io() to make sure we don't panic when we get an error.
    I also spot checked all the other instances of checking mirror_ds and we
    appear to be doing the correct checks everywhere, only unconditionally
    dereferencing mirror_ds when we know it would be valid.
    
    Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
    Fixes: b739a5bd9d9f ("NFSv4/flexfiles: Cancel I/O if the layout is recalled or revoked")
    Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
    Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/nfs/flexfilelayout/flexfilelayout.c b/fs/nfs/flexfilelayout/flexfilelayout.c
index 81bbafab18a99..4376881be7918 100644
--- a/fs/nfs/flexfilelayout/flexfilelayout.c
+++ b/fs/nfs/flexfilelayout/flexfilelayout.c
@@ -2016,7 +2016,7 @@ static void ff_layout_cancel_io(struct pnfs_layout_segment *lseg)
 	for (idx = 0; idx < flseg->mirror_array_cnt; idx++) {
 		mirror = flseg->mirror_array[idx];
 		mirror_ds = mirror->mirror_ds;
-		if (!mirror_ds)
+		if (IS_ERR_OR_NULL(mirror_ds))
 			continue;
 		ds = mirror->mirror_ds->ds;
 		if (!ds)




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