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Mallory
Medium

Linux kernel F2FS NULL pointer dereference in mount-time truncation path (f2fs_disable_checkpoint/f2fs_gc)

IdentifiersCVE-2024-43859CWE-476· NULL Pointer Dereference

A Linux kernel F2FS bug (fixed upstream) can trigger a NULL pointer dereference during a mount-time code path involving checkpoint disablement and garbage collection. Specifically, during mount the sequence f2fs_fill_super() → f2fs_disable_checkpoint() → f2fs_gc() → f2fs_iget() → f2fs_truncate() can reach fscrypt_set_bio_crypt_ctx() via f2fs_do_truncate_blocks()/truncate_partial_data_page(), but inode->i_crypt_info is not initialized in this path, leading to a NULL dereference. The fix relocates truncation of preallocated blocks to f2fs_file_open(), after fscrypt_file_open(), ensuring the encryption context is initialized before use.

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ANALYST BRIEF

Impact, mitigation & remediation

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Impact

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Kernel crash/denial of service via NULL pointer dereference in fscrypt_set_bio_crypt_ctx() reachable from F2FS mount-time operations; depending on deployment and threat model this is tracked as a kernel elevation-of-privilege class issue in Android’s bulletin, but the provided content specifically evidences a NULL dereference leading to a crash.

Mitigation

If you can’t patch tonight, do this now.

Avoid mounting/using affected F2FS configurations in environments where untrusted actors can trigger the vulnerable mount/GC/truncation path; reduce exposure by restricting who can mount filesystems / supply F2FS images and by disabling or limiting use of F2FS with fscrypt until patched (where operationally feasible).

Remediation

Patch, then assume compromise.

Apply the Linux kernel patch that moves truncation of preallocated blocks to f2fs_file_open() after fscrypt_file_open() (i.e., kernels containing the upstream fix for CVE-2024-43859). For Android, update to a security patch level that includes CVE-2024-43859 (listed under 2026-03-05 in the referenced bulletin).
PUBLIC EXPLOITS

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VALID 0 / 0 TOTALView more in app

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LinuxLinux Kerneloperating_system

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