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As report by Wenqing Liu in bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=215231 - Overview kernel NULL pointer dereference triggered in folio_mark_dirty() when mount and operate on a crafted f2fs image - Reproduce tested on kernel 5.16-rc3, 5.15.X under root 1. mkdir mnt 2. mount -t f2fs tmp1.img mnt 3. touch tmp 4. cp tmp mnt F2FS-fs (loop0): sanity_check_inode: inode (ino=49) extent info [5942, 4294180864, 4] is incorrect, run fsck to fix F2FS-fs (loop0): f2fs_check_nid_range: out-of-range nid=31340049, run fsck to fix. BUG: kernel NULL pointer dereference, address: 0000000000000000 folio_mark_dirty+0x33/0x50 move_data_page+0x2dd/0x460 [f2fs] do_garbage_collect+0xc18/0x16a0 [f2fs] f2fs_gc+0x1d3/0xd90 [f2fs] f2fs_balance_fs+0x13a/0x570 [f2fs] f2fs_create+0x285/0x840 [f2fs] path_openat+0xe6d/0x1040 do_filp_open+0xc5/0x140 do_sys_openat2+0x23a/0x310 do_sys_open+0x57/0x80 The root cause is for special file: e.g. character, block, fifo or socket file, f2fs doesn't assign address space operations pointer array for mapping->a_ops field, so, in a fuzzed image, SSA table indicates a data block belong to special file, when f2fs tries to migrate that block, it causes NULL pointer access once move_data_page() calls a_ops->set_dirty_page(). Cc: stable@vger.kernel.org Reported-by: Wenqing Liu <wenqingliu0120@gmail.com> Signed-off-by: Chao Yu <chao@kernel.org> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
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https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.