FAILED: patch "[PATCH] btrfs: fix transaction abort on file creation due to name" failed to apply to 6.6-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 2d1ababdedd4ba38867c2500eb7f95af5ddeeef7
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026031721-flask-submersed-ea9b@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 2d1ababdedd4ba38867c2500eb7f95af5ddeeef7 Mon Sep 17 00:00:00 2001
From: Filipe Manana <fdmanana@suse.com>
Date: Thu, 26 Feb 2026 11:05:43 +0000
Subject: [PATCH] btrfs: fix transaction abort on file creation due to name
 hash collision

If we attempt to create several files with names that result in the same
hash, we have to pack them in same dir item and that has a limit inherent
to the leaf size. However if we reach that limit, we trigger a transaction
abort and turns the filesystem into RO mode. This allows for a malicious
user to disrupt a system, without the need to have administration
privileges/capabilities.

Reproducer:

  $ cat exploit-hash-collisions.sh
  #!/bin/bash

  DEV=/dev/sdi
  MNT=/mnt/sdi

  # Use smallest node size to make the test faster and require fewer file
  # names that result in hash collision.
  mkfs.btrfs -f --nodesize 4K $DEV
  mount $DEV $MNT

  # List of names that result in the same crc32c hash for btrfs.
  declare -a names=(
   'foobar'
   '%a8tYkxfGMLWRGr55QSeQc4PBNH9PCLIvR6jZnkDtUUru1t@RouaUe_L:@xGkbO3nCwvLNYeK9vhE628gss:T$yZjZ5l-Nbd6CbC$M=hqE-ujhJICXyIxBvYrIU9-TDC'
   'AQci3EUB%shMsg-N%frgU:02ByLs=IPJU0OpgiWit5nexSyxZDncY6WB:=zKZuk5Zy0DD$Ua78%MelgBuMqaHGyKsJUFf9s=UW80PcJmKctb46KveLSiUtNmqrMiL9-Y0I_l5Fnam04CGIg=8@U:Z'
   'CvVqJpJzueKcuA$wqwePfyu7VxuWNN3ho$p0zi2H8QFYK$7YlEqOhhb%:hHgjhIjW5vnqWHKNP4'
   'ET:vk@rFU4tsvMB0$C_p=xQHaYZjvoF%-BTc%wkFW8yaDAPcCYoR%x$FH5O:'
   'HwTon%v7SGSP4FE08jBwwiu5aot2CFKXHTeEAa@38fUcNGOWvE@Mz6WBeDH_VooaZ6AgsXPkVGwy9l@@ZbNXabUU9csiWrrOp0MWUdfi$EZ3w9GkIqtz7I_eOsByOkBOO'
   'Ij%2VlFGXSuPvxJGf5UWy6O@1svxGha%b@=%wjkq:CIgE6u7eJOjmQY5qTtxE2Rjbis9@us'
   'KBkjG5%9R8K9sOG8UTnAYjxLNAvBmvV5vz3IiZaPmKuLYO03-6asI9lJ_j4@6Xo$KZicaLWJ3Pv8XEwVeUPMwbHYWwbx0pYvNlGMO9F:ZhHAwyctnGy%_eujl%WPd4U2BI7qooOSr85J-C2V$LfY'
   'NcRfDfuUQ2=zP8K3CCF5dFcpfiOm6mwenShsAb_F%n6GAGC7fT2JFFn:c35X-3aYwoq7jNX5$ZJ6hI3wnZs$7KgGi7wjulffhHNUxAT0fRRLF39vJ@NvaEMxsMO'
   'Oj42AQAEzRoTxa5OuSKIr=A_lwGMy132v4g3Pdq1GvUG9874YseIFQ6QU'
   'Ono7avN5GjC:_6dBJ_'
   'WHmN2gnmaN-9dVDy4aWo:yNGFzz8qsJyJhWEWcud7$QzN2D9R0efIWWEdu5kwWr73NZm4=@CoCDxrrZnRITr-kGtU_cfW2:%2_am'
   'WiFnuTEhAG9FEC6zopQmj-A-$LDQ0T3WULz%ox3UZAPybSV6v1Z$b4L_XBi4M4BMBtJZpz93r9xafpB77r:lbwvitWRyo$odnAUYlYMmU4RvgnNd--e=I5hiEjGLETTtaScWlQp8mYsBovZwM2k'
   'XKyH=OsOAF3p%uziGF_ZVr$ivrvhVgD@1u%5RtrV-gl_vqAwHkK@x7YwlxX3qT6WKKQ%PR56NrUBU2dOAOAdzr2=5nJuKPM-T-$ZpQfCL7phxQbUcb:BZOTPaFExc-qK-gDRCDW2'
   'd3uUR6OFEwZr%ns1XH_@tbxA@cCPmbBRLdyh7p6V45H$P2$F%w0RqrD3M0g8aGvWpoTFMiBdOTJXjD:JF7=h9a_43xBywYAP%r$SPZi%zDg%ql-KvkdUCtF9OLaQlxmd'
   'ePTpbnit%hyNm@WELlpKzNZYOzOTf8EQ$sEfkMy1VOfIUu3coyvIr13-Y7Sv5v-Ivax2Go_GQRFMU1b3362nktT9WOJf3SpT%z8sZmM3gvYQBDgmKI%%RM-G7hyrhgYflOw%z::ZRcv5O:lDCFm'
   'evqk743Y@dvZAiG5J05L_ROFV@$2%rVWJ2%3nxV72-W7$e$-SK3tuSHA2mBt$qloC5jwNx33GmQUjD%akhBPu=VJ5g$xhlZiaFtTrjeeM5x7dt4cHpX0cZkmfImndYzGmvwQG:$euFYmXn$_2rA9mKZ'
   'gkgUtnihWXsZQTEkrMAWIxir09k3t7jk_IK25t1:cy1XWN0GGqC%FrySdcmU7M8MuPO_ppkLw3=Dfr0UuBAL4%GFk2$Ma10V1jDRGJje%Xx9EV2ERaWKtjpwiZwh0gCSJsj5UL7CR8RtW5opCVFKGGy8Cky'
   'hNgsG_8lNRik3PvphqPm0yEH3P%%fYG:kQLY=6O-61Wa6nrV_WVGR6TLB09vHOv%g4VQRP8Gzx7VXUY1qvZyS'
   'isA7JVzN12xCxVPJZ_qoLm-pTBuhjjHMvV7o=F:EaClfYNyFGlsfw-Kf%uxdqW-kwk1sPl2vhbjyHU1A6$hz'
   'kiJ_fgcdZFDiOptjgH5PN9-PSyLO4fbk_:u5_2tz35lV_iXiJ6cx7pwjTtKy-XGaQ5IefmpJ4N_ZqGsqCsKuqOOBgf9LkUdffHet@Wu'
   'lvwtxyhE9:%Q3UxeHiViUyNzJsy:fm38pg_b6s25JvdhOAT=1s0$pG25x=LZ2rlHTszj=gN6M4zHZYr_qrB49i=pA--@WqWLIuX7o1S_SfS@2FSiUZN'
   'rC24cw3UBDZ=5qJBUMs9e$=S4Y94ni%Z8639vnrGp=0Hv4z3dNFL0fBLmQ40=EYIY:Z=SLc@QLMSt2zsss2ZXrP7j4='
   'uwGl2s-fFrf@GqS=DQqq2I0LJSsOmM%xzTjS:lzXguE3wChdMoHYtLRKPvfaPOZF2fER@j53evbKa7R%A7r4%YEkD=kicJe@SFiGtXHbKe4gCgPAYbnVn'
   'UG37U6KKua2bgc:IHzRs7BnB6FD:2Mt5Cc5NdlsW%$1tyvnfz7S27FvNkroXwAW:mBZLA1@qa9WnDbHCDmQmfPMC9z-Eq6QT0jhhPpqyymaD:R02ghwYo%yx7SAaaq-:x33LYpei$5g8DMl3C'
   'y2vjek0FE1PDJC0qpfnN:x8k2wCFZ9xiUF2ege=JnP98R%wxjKkdfEiLWvQzmnW'
   '8-HCSgH5B%K7P8_jaVtQhBXpBk:pE-$P7ts58U0J@iR9YZntMPl7j$s62yAJO@_9eanFPS54b=UTw$94C-t=HLxT8n6o9P=QnIxq-f1=Ne2dvhe6WbjEQtc'
   'YPPh:IFt2mtR6XWSmjHptXL_hbSYu8bMw-JP8@PNyaFkdNFsk$M=xfL6LDKCDM-mSyGA_2MBwZ8Dr4=R1D%7-mCaaKGxb990jzaagRktDTyp'
   '9hD2ApKa_t_7x-a@GCG28kY:7$M@5udI1myQ$x5udtggvagmCQcq9QXWRC5hoB0o-_zHQUqZI5rMcz_kbMgvN5jr63LeYA4Cj-c6F5Ugmx6DgVf@2Jqm%MafecpgooqreJ53P-QTS'
  )

  # Now create files with all those names in the same parent directory.
  # It should not fail since a 4K leaf has enough space for them.
  for name in "${names[@]}"; do
       touch $MNT/$name
  done

  # Now add one more file name that causes a crc32c hash collision.
  # This should fail, but it should not turn the filesystem into RO mode
  # (which could be exploited by malicious users) due to a transaction
  # abort.
  touch $MNT/'W6tIm-VK2@BGC@IBfcgg6j_p:pxp_QUqtWpGD5Ok_GmijKOJJt'

  # Check that we are able to create another file, with a name that does not cause
  # a crc32c hash collision.
  echo -n "hello world" > $MNT/baz

  # Unmount and mount again, verify file baz exists and with the right content.
  umount $MNT
  mount $DEV $MNT
  echo "File baz content: $(cat $MNT/baz)"

  umount $MNT

When running the reproducer:

  $ ./exploit-hash-collisions.sh
  (...)
  touch: cannot touch '/mnt/sdi/W6tIm-VK2@BGC@IBfcgg6j_p:pxp_QUqtWpGD5Ok_GmijKOJJt': Value too large for defined data type
  ./exploit-hash-collisions.sh: line 57: /mnt/sdi/baz: Read-only file system
  cat: /mnt/sdi/baz: No such file or directory
  File baz content:

And the transaction abort stack trace in dmesg/syslog:

  $ dmesg
  (...)
  [758240.509761] ------------[ cut here ]------------
  [758240.510668] BTRFS: Transaction aborted (error -75)
  [758240.511577] WARNING: fs/btrfs/inode.c:6854 at btrfs_create_new_inode+0x805/0xb50 [btrfs], CPU#6: touch/888644
  [758240.513513] Modules linked in: btrfs dm_zero (...)
  [758240.523221] CPU: 6 UID: 0 PID: 888644 Comm: touch Tainted: G        W           6.19.0-rc8-btrfs-next-225+ #1 PREEMPT(full)
  [758240.524621] Tainted: [W]=WARN
  [758240.525037] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.2-0-gea1b7a073390-prebuilt.qemu.org 04/01/2014
  [758240.526331] RIP: 0010:btrfs_create_new_inode+0x80b/0xb50 [btrfs]
  [758240.527093] Code: 0f 82 cf (...)
  [758240.529211] RSP: 0018:ffffce64418fbb48 EFLAGS: 00010292
  [758240.529935] RAX: 00000000ffffffd3 RBX: 0000000000000000 RCX: 00000000ffffffb5
  [758240.531040] RDX: 0000000d04f33e06 RSI: 00000000ffffffb5 RDI: ffffffffc0919dd0
  [758240.531920] RBP: ffffce64418fbc10 R08: 0000000000000000 R09: 00000000ffffffb5
  [758240.532928] R10: 0000000000000000 R11: ffff8e52c0000000 R12: ffff8e53eee7d0f0
  [758240.533818] R13: ffff8e57f70932a0 R14: ffff8e5417629568 R15: 0000000000000000
  [758240.534664] FS:  00007f1959a2a740(0000) GS:ffff8e5b27cae000(0000) knlGS:0000000000000000
  [758240.535821] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  [758240.536644] CR2: 00007f1959b10ce0 CR3: 000000012a2cc005 CR4: 0000000000370ef0
  [758240.537517] Call Trace:
  [758240.537828]  <TASK>
  [758240.538099]  btrfs_create_common+0xbf/0x140 [btrfs]
  [758240.538760]  path_openat+0x111a/0x15b0
  [758240.539252]  do_filp_open+0xc2/0x170
  [758240.539699]  ? preempt_count_add+0x47/0xa0
  [758240.540200]  ? __virt_addr_valid+0xe4/0x1a0
  [758240.540800]  ? __check_object_size+0x1b3/0x230
  [758240.541661]  ? alloc_fd+0x118/0x180
  [758240.542315]  do_sys_openat2+0x70/0xd0
  [758240.543012]  __x64_sys_openat+0x50/0xa0
  [758240.543723]  do_syscall_64+0x50/0xf20
  [758240.544462]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
  [758240.545397] RIP: 0033:0x7f1959abc687
  [758240.546019] Code: 48 89 fa (...)
  [758240.548522] RSP: 002b:00007ffe16ff8690 EFLAGS: 00000202 ORIG_RAX: 0000000000000101
  [758240.566278] RAX: ffffffffffffffda RBX: 00007f1959a2a740 RCX: 00007f1959abc687
  [758240.567068] RDX: 0000000000000941 RSI: 00007ffe16ffa333 RDI: ffffffffffffff9c
  [758240.567860] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
  [758240.568707] R10: 00000000000001b6 R11: 0000000000000202 R12: 0000561eec7c4b90
  [758240.569712] R13: 0000561eec7c311f R14: 00007ffe16ffa333 R15: 0000000000000000
  [758240.570758]  </TASK>
  [758240.571040] ---[ end trace 0000000000000000 ]---
  [758240.571681] BTRFS: error (device sdi state A) in btrfs_create_new_inode:6854: errno=-75 unknown
  [758240.572899] BTRFS info (device sdi state EA): forced readonly

Fix this by checking for hash collision, and if the adding a new name is
possible, early in btrfs_create_new_inode() before we do any tree updates,
so that we don't need to abort the transaction if we cannot add the new
name due to the leaf size limit.

A test case for fstests will be sent soon.

Fixes: caae78e03234 ("btrfs: move common inode creation code into btrfs_create_new_inode()")
CC: stable@vger.kernel.org # 6.1+
Reviewed-by: Boris Burkov <boris@bur.io>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index d28d55beaacd..b409efe1857e 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -6610,6 +6610,25 @@ int btrfs_create_new_inode(struct btrfs_trans_handle *trans,
 	int ret;
 	bool xa_reserved = false;
 
+	if (!args->orphan && !args->subvol) {
+		/*
+		 * Before anything else, check if we can add the name to the
+		 * parent directory. We want to avoid a dir item overflow in
+		 * case we have an existing dir item due to existing name
+		 * hash collisions. We do this check here before we call
+		 * btrfs_add_link() down below so that we can avoid a
+		 * transaction abort (which could be exploited by malicious
+		 * users).
+		 *
+		 * For subvolumes we already do this in btrfs_mksubvol().
+		 */
+		ret = btrfs_check_dir_item_collision(BTRFS_I(dir)->root,
+						     btrfs_ino(BTRFS_I(dir)),
+						     name);
+		if (ret < 0)
+			return ret;
+	}
+
 	path = btrfs_alloc_path();
 	if (!path)
 		return -ENOMEM;