kernel/linux.git/fs/ext4/sysfs.c, branch v5.15.208

ext4: fix use-after-free in update_super_work when racing with umount

2026-04-18T08:33:38+00:00

[ Upstream commit d15e4b0a418537aafa56b2cb80d44add83e83697 ] Commit b98535d09179 ("ext4: fix bug_on in start_this_handle during umount filesystem") moved ext4_unregister_sysfs() before flushing s_sb_upd_work to prevent new error work from being queued via /proc/fs/ext4/xx/mb_groups reads during unmount. However, this introduced a use-after-free because update_super_work calls ext4_notify_error_sysfs() -> sysfs_notify() which accesses the kobject's kernfs_node after it has been freed by kobject_del() in ext4_unregister_sysfs(): update_super_work ext4_put_super ----------------- -------------- ext4_unregister_sysfs(sb) kobject_del(&sbi->s_kobj) __kobject_del() sysfs_remove_dir() kobj->sd = NULL sysfs_put(sd) kernfs_put() // RCU free ext4_notify_error_sysfs(sbi) sysfs_notify(&sbi->s_kobj) kn = kobj->sd // stale pointer kernfs_get(kn) // UAF on freed kernfs_node ext4_journal_destroy() flush_work(&sbi->s_sb_upd_work) Instead of reordering the teardown sequence, fix this by making ext4_notify_error_sysfs() detect that sysfs has already been torn down by checking s_kobj.state_in_sysfs, and skipping the sysfs_notify() call in that case. A dedicated mutex (s_error_notify_mutex) serializes ext4_notify_error_sysfs() against kobject_del() in ext4_unregister_sysfs() to prevent TOCTOU races where the kobject could be deleted between the state_in_sysfs check and the sysfs_notify() call. Fixes: b98535d09179 ("ext4: fix bug_on in start_this_handle during umount filesystem") Cc: Jiayuan Chen Suggested-by: Jan Kara Signed-off-by: Jiayuan Chen Reviewed-by: Ritesh Harjani (IBM) Reviewed-by: Jan Kara Link: https://patch.msgid.link/20260319120336.157873-1-jiayuan.chen@linux.dev Signed-off-by: Theodore Ts'o Cc: stable@kernel.org [ adapted mutex_init placement ] Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

ext4: Fix function prototype mismatch for ext4_feat_ktype

2023-02-25T11:06:45+00:00

commit 118901ad1f25d2334255b3d50512fa20591531cd upstream. With clang's kernel control flow integrity (kCFI, CONFIG_CFI_CLANG), indirect call targets are validated against the expected function pointer prototype to make sure the call target is valid to help mitigate ROP attacks. If they are not identical, there is a failure at run time, which manifests as either a kernel panic or thread getting killed. ext4_feat_ktype was setting the "release" handler to "kfree", which doesn't have a matching function prototype. Add a simple wrapper with the correct prototype. This was found as a result of Clang's new -Wcast-function-type-strict flag, which is more sensitive than the simpler -Wcast-function-type, which only checks for type width mismatches. Note that this code is only reached when ext4 is a loadable module and it is being unloaded: CFI failure at kobject_put+0xbb/0x1b0 (target: kfree+0x0/0x180; expected type: 0x7c4aa698) ... RIP: 0010:kobject_put+0xbb/0x1b0 ... Call Trace: ext4_exit_sysfs+0x14/0x60 [ext4] cleanup_module+0x67/0xedb [ext4] Fixes: b99fee58a20a ("ext4: create ext4_feat kobject dynamically") Cc: Theodore Ts'o Cc: Eric Biggers Cc: stable@vger.kernel.org Build-tested-by: Gustavo A. R. Silva Reviewed-by: Gustavo A. R. Silva Reviewed-by: Nathan Chancellor Link: https://lore.kernel.org/r/20230103234616.never.915-kees@kernel.org Signed-off-by: Kees Cook Reviewed-by: Eric Biggers Link: https://lore.kernel.org/r/20230104210908.gonna.388-kees@kernel.org Signed-off-by: Greg Kroah-Hartman

ext4: notify sysfs on errors_count value change

2021-06-30T01:06:02+00:00

After s_error_count is incremented, signal the change in the corresponding sysfs attribute via sysfs_notify. This allows userspace to poll() on changes to /sys/fs/ext4/*/errors_count. [ Moved call of ext4_notify_error_sysfs() to flush_stashed_error_work() to avoid BUG's caused by calling sysfs_notify trying to sleep after being called from an invalid context. -- TYT ] Signed-off-by: Jonathan Davies Link: https://lore.kernel.org/r/20210611140209.28903-1-jonathan.davies@nutanix.com Signed-off-by: Theodore Ts'o

ext4: Only advertise encrypted_casefold when encryption and unicode are enabled

2021-06-06T14:10:23+00:00

Encrypted casefolding is only supported when both encryption and casefolding are both enabled in the config. Fixes: 471fbbea7ff7 ("ext4: handle casefolding with encryption") Cc: stable@vger.kernel.org # 5.13+ Signed-off-by: Daniel Rosenberg Link: https://lore.kernel.org/r/20210603094849.314342-1-drosen@google.com Signed-off-by: Theodore Ts'o

ext4: add proc files to monitor new structures

2021-04-09T15:34:59+00:00

This patch adds a new file "mb_structs_summary" which allows us to see the summary of the new allocator structures added in this series. Here's the sample output of file: optimize_scan: 1 max_free_order_lists: list_order_0_groups: 0 list_order_1_groups: 0 list_order_2_groups: 0 list_order_3_groups: 0 list_order_4_groups: 0 list_order_5_groups: 0 list_order_6_groups: 0 list_order_7_groups: 0 list_order_8_groups: 0 list_order_9_groups: 0 list_order_10_groups: 0 list_order_11_groups: 0 list_order_12_groups: 0 list_order_13_groups: 40 fragment_size_tree: tree_min: 16384 tree_max: 32768 tree_nodes: 40 Signed-off-by: Harshad Shirwadkar Reviewed-by: Andreas Dilger Reviewed-by: Ritesh Harjani Link: https://lore.kernel.org/r/20210401172129.189766-7-harshadshirwadkar@gmail.com Signed-off-by: Theodore Ts'o

ext4: improve cr 0 / cr 1 group scanning

2021-04-09T15:34:59+00:00

Instead of traversing through groups linearly, scan groups in specific orders at cr 0 and cr 1. At cr 0, we want to find groups that have the largest free order >= the order of the request. So, with this patch, we maintain lists for each possible order and insert each group into a list based on the largest free order in its buddy bitmap. During cr 0 allocation, we traverse these lists in the increasing order of largest free orders. This allows us to find a group with the best available cr 0 match in constant time. If nothing can be found, we fallback to cr 1 immediately. At CR1, the story is slightly different. We want to traverse in the order of increasing average fragment size. For CR1, we maintain a rb tree of groupinfos which is sorted by average fragment size. Instead of traversing linearly, at CR1, we traverse in the order of increasing average fragment size, starting at the most optimal group. This brings down cr 1 search complexity to log(num groups). For cr >= 2, we just perform the linear search as before. Also, in case of lock contention, we intermittently fallback to linear search even in CR 0 and CR 1 cases. This allows us to proceed during the allocation path even in case of high contention. There is an opportunity to do optimization at CR2 too. That's because at CR2 we only consider groups where bb_free counter (number of free blocks) is greater than the request extent size. That's left as future work. All the changes introduced in this patch are protected under a new mount option "mb_optimize_scan". With this patchset, following experiment was performed: Created a highly fragmented disk of size 65TB. The disk had no contiguous 2M regions. Following command was run consecutively for 3 times: time dd if=/dev/urandom of=file bs=2M count=10 Here are the results with and without cr 0/1 optimizations introduced in this patch: |---------+------------------------------+---------------------------| | | Without CR 0/1 Optimizations | With CR 0/1 Optimizations | |---------+------------------------------+---------------------------| | 1st run | 5m1.871s | 2m47.642s | | 2nd run | 2m28.390s | 0m0.611s | | 3rd run | 2m26.530s | 0m1.255s | |---------+------------------------------+---------------------------| Signed-off-by: Harshad Shirwadkar Reported-by: kernel test robot Reported-by: Dan Carpenter Reviewed-by: Andreas Dilger Link: https://lore.kernel.org/r/20210401172129.189766-6-harshadshirwadkar@gmail.com Signed-off-by: Theodore Ts'o

ext4: add mballoc stats proc file

2021-04-09T15:34:59+00:00

Add new stats for measuring the performance of mballoc. This patch is forked from Artem Blagodarenko's work that can be found here: https://github.com/lustre/lustre-release/blob/master/ldiskfs/kernel_patches/patches/rhel8/ext4-simple-blockalloc.patch This patch reorganizes the stats by cr level. This is how the output looks like: mballoc: reqs: 0 success: 0 groups_scanned: 0 cr0_stats: hits: 0 groups_considered: 0 useless_loops: 0 bad_suggestions: 0 cr1_stats: hits: 0 groups_considered: 0 useless_loops: 0 bad_suggestions: 0 cr2_stats: hits: 0 groups_considered: 0 useless_loops: 0 cr3_stats: hits: 0 groups_considered: 0 useless_loops: 0 extents_scanned: 0 goal_hits: 0 2^n_hits: 0 breaks: 0 lost: 0 buddies_generated: 0/40 buddies_time_used: 0 preallocated: 0 discarded: 0 Signed-off-by: Harshad Shirwadkar Reviewed-by: Andreas Dilger Reviewed-by: Ritesh Harjani Link: https://lore.kernel.org/r/20210401172129.189766-4-harshadshirwadkar@gmail.com Signed-off-by: Theodore Ts'o

ext4: handle casefolding with encryption

2021-04-06T02:04:20+00:00

This adds support for encryption with casefolding. Since the name on disk is case preserving, and also encrypted, we can no longer just recompute the hash on the fly. Additionally, to avoid leaking extra information from the hash of the unencrypted name, we use siphash via an fscrypt v2 policy. The hash is stored at the end of the directory entry for all entries inside of an encrypted and casefolded directory apart from those that deal with '.' and '..'. This way, the change is backwards compatible with existing ext4 filesystems. [ Changed to advertise this feature via the file: /sys/fs/ext4/features/encrypted_casefold -- TYT ] Signed-off-by: Daniel Rosenberg Reviewed-by: Andreas Dilger Link: https://lore.kernel.org/r/20210319073414.1381041-2-drosen@google.com Signed-off-by: Theodore Ts'o

ext4: shrink race window in ext4_should_retry_alloc()

2021-03-06T16:56:10+00:00

When generic/371 is run on kvm-xfstests using 5.10 and 5.11 kernels, it fails at significant rates on the two test scenarios that disable delayed allocation (ext3conv and data_journal) and force actual block allocation for the fallocate and pwrite functions in the test. The failure rate on 5.10 for both ext3conv and data_journal on one test system typically runs about 85%. On 5.11, the failure rate on ext3conv sometimes drops to as low as 1% while the rate on data_journal increases to nearly 100%. The observed failures are largely due to ext4_should_retry_alloc() cutting off block allocation retries when s_mb_free_pending (used to indicate that a transaction in progress will free blocks) is 0. However, free space is usually available when this occurs during runs of generic/371. It appears that a thread attempting to allocate blocks is just missing transaction commits in other threads that increase the free cluster count and reset s_mb_free_pending while the allocating thread isn't running. Explicitly testing for free space availability avoids this race. The current code uses a post-increment operator in the conditional expression that determines whether the retry limit has been exceeded. This means that the conditional expression uses the value of the retry counter before it's increased, resulting in an extra retry cycle. The current code actually retries twice before hitting its retry limit rather than once. Increasing the retry limit to 3 from the current actual maximum retry count of 2 in combination with the change described above reduces the observed failure rate to less that 0.1% on both ext3conv and data_journal with what should be limited impact on users sensitive to the overhead caused by retries. A per filesystem percpu counter exported via sysfs is added to allow users or developers to track the number of times the retry limit is exceeded without resorting to debugging methods. This should provide some insight into worst case retry behavior. Signed-off-by: Eric Whitney Link: https://lore.kernel.org/r/20210218151132.19678-1-enwlinux@gmail.com Signed-off-by: Theodore Ts'o

block: switch partition lookup to use struct block_device

2020-12-01T21:53:40+00:00

Use struct block_device to lookup partitions on a disk. This removes all usage of struct hd_struct from the I/O path. Signed-off-by: Christoph Hellwig Reviewed-by: Jan Kara Reviewed-by: Hannes Reinecke Acked-by: Coly Li [bcache] Acked-by: Chao Yu [f2fs] Signed-off-by: Jens Axboe