cbcvebase.
CVE-2024-35784
published 2024-05-17

CVE-2024-35784: In the Linux kernel, the following vulnerability has been resolved: btrfs: fix deadlock with fiemap and extent locking While working on the patchset to remove…

PriorityP419medium5.5CVSS 3.1
AVLACLPRLUINSUCNINAH
EPSS
0.17%
7.0th percentile
In the Linux kernel, the following vulnerability has been resolved: btrfs: fix deadlock with fiemap and extent locking While working on the patchset to remove extent locking I got a lockdep splat with fiemap and pagefaulting with my new extent lock replacement lock. This deadlock exists with our normal code, we just don't have lockdep annotations with the extent locking so we've never noticed it. Since we're copying the fiemap extent to user space on every iteration we have the chance of pagefaulting. Because we hold the extent lock for the entire range we could mkwrite into a range in the file that we have mmap'ed. This would deadlock with the following stack trace [] lock_extent+0x28d/0x2f0 [] btrfs_page_mkwrite+0x273/0x8a0 [] do_page_mkwrite+0x50/0xb0 [] do_fault+0xc1/0x7b0 [] __handle_mm_fault+0x2fa/0x460 [] handle_mm_fault+0xa4/0x330 [] do_user_addr_fault+0x1f4/0x800 [] exc_page_fault+0x7c/0x1e0 [] asm_exc_page_fault+0x26/0x30 [] rep_movs_alternative+0x33/0x70 [] _copy_to_user+0x49/0x70 [] fiemap_fill_next_extent+0xc8/0x120 [] emit_fiemap_extent+0x4d/0xa0 [] extent_fiemap+0x7f8/0xad0 [] btrfs_fiemap+0x49/0x80 [] __x64_sys_ioctl+0x3e1/0xb50 [] do_syscall_64+0x94/0x1a0 [] entry_SYSCALL_64_after_hwframe+0x6e/0x76 I wrote an fstest to reproduce this deadlock without my replacement lock and verified that the deadlock exists with our existing locking. To fix this simply don't take the extent lock for the entire duration of the fiemap. This is safe in general because we keep track of where we are when we're searching the tree, so if an ordered extent updates in the middle of our fiemap call we'll still emit the correct extents because we know what offset we were on before. The only place we maintain the lock is searching delalloc. Since the delalloc stuff can change during writeback we want to lock the extent range so we have a consistent view of delalloc at the time we're checking to see if we need to set the delalloc flag. With this patch applied we no long

Affected

13 ranges
VendorProductVersion rangeFixed in
debianlinux< linux 6.7.12-1 (forky)linux 6.7.12-1 (forky)
linuxlinux——
linuxlinux>= 1506fcc8189cdd4b95e06df7845a09f18b4526a6 < ded566b4637f1b6b4c9ba74e7d0b8493e93f19cfded566b4637f1b6b4c9ba74e7d0b8493e93f19cf
linuxlinux>= 1506fcc8189cdd4b95e06df7845a09f18b4526a6 < 89bca7fe6382d61e88c67a0b0e7bce315986fb8b89bca7fe6382d61e88c67a0b0e7bce315986fb8b
linuxlinux>= 1506fcc8189cdd4b95e06df7845a09f18b4526a6 < b0ad381fa7690244802aed119b478b4bdafc31ddb0ad381fa7690244802aed119b478b4bdafc31dd
linuxlinux_kernel< 6.6.246.6.24
linuxlinux_kernel——
linuxlinux_kernel>= 0 < 6.7.12-16.7.12-1
linuxlinux_kernel>= 0 < 6.7.12-16.7.12-1
linuxlinux_kernel>= 6.7 < 6.7.126.7.12
msrccbl2_kernel_5.15.186.1-1_on_cbl_mariner_2.0——
msrccbl2_kernel_5.15.200.1-1_on_cbl_mariner_2.0——
msrccbl2_kernel_5.15.202.1-1_on_cbl_mariner_2.0——

CVSS provenance

nvdv3.15.5MEDIUMCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
osv5.5MEDIUM
vendor_debian5.5MEDIUM
vendor_msrc5.5MEDIUM
vendor_redhat5.5MEDIUM
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