CVE-2024-38578

In the Linux kernel, the following vulnerability has been resolved:

ecryptfs: Fix buffer size for tag 66 packet

The TAG 66 Packet Format description is missing the cipher code and checksum fields that are packed into the message packet. As a result, the buffer allocated for the packet is 3 bytes too small and write_tag_66_packet() will write up to 3 bytes past the end of the buffer.

Fix this by increasing the size of the allocation so the whole packet will always fit in the buffer.

This fixes the below kasan slab-out-of-bounds bug:

BUG: KASAN: slab-out-of-bounds in ecryptfs_generate_key_packet_set+0x7d6/0xde0 Write of size 1 at addr ffff88800afbb2a5 by task touch/181

CPU: 0 PID: 181 Comm: touch Not tainted 6.6.13-gnu #1 4c9534092be820851bb687b82d1f92a426598dc6 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2/GNU Guix 04/01/2014 Call Trace: dump_stack_lvl+0x4c/0x70 print_report+0xc5/0x610 ? ecryptfs_generate_key_packet_set+0x7d6/0xde0 ? kasan_complete_mode_report_info+0x44/0x210 ? ecryptfs_generate_key_packet_set+0x7d6/0xde0 kasan_report+0xc2/0x110 ? ecryptfs_generate_key_packet_set+0x7d6/0xde0 __asan_store1+0x62/0x80 ecryptfs_generate_key_packet_set+0x7d6/0xde0 ? __pfx_ecryptfs_generate_key_packet_set+0x10/0x10 ? __alloc_pages+0x2e2/0x540 ? __pfx_ovl_open+0x10/0x10 [overlay 30837f11141636a8e1793533a02e6e2e885dad1d] ? dentry_open+0x8f/0xd0 ecryptfs_write_metadata+0x30a/0x550 ? __pfx_ecryptfs_write_metadata+0x10/0x10 ? ecryptfs_get_lower_file+0x6b/0x190 ecryptfs_initialize_file+0x77/0x150 ecryptfs_create+0x1c2/0x2f0 path_openat+0x17cf/0x1ba0 ? __pfx_path_openat+0x10/0x10 do_filp_open+0x15e/0x290 ? __pfx_do_filp_open+0x10/0x10 ? __kasan_check_write+0x18/0x30 ? _raw_spin_lock+0x86/0xf0 ? __pfx__raw_spin_lock+0x10/0x10 ? __kasan_check_write+0x18/0x30 ? alloc_fd+0xf4/0x330 do_sys_openat2+0x122/0x160 ? __pfx_do_sys_openat2+0x10/0x10 __x64_sys_openat+0xef/0x170 ? __pfx___x64_sys_openat+0x10/0x10 do_syscall_64+0x60/0xd0 entry_SYSCALL_64_after_hwframe+0x6e/0xd8 RIP: 0033:0x7f00a703fd67 Code: 25 00 00 41 00 3d 00 00 41 00 74 37 64 8b 04 25 18 00 00 00 85 c0 75 5b 44 89 e2 48 89 ee bf 9c ff ff ff b8 01 01 00 00 0f 05 <48> 3d 00 f0 ff ff 0f 87 85 00 00 00 48 83 c4 68 5d 41 5c c3 0f 1f RSP: 002b:00007ffc088e30b0 EFLAGS: 00000246 ORIG_RAX: 0000000000000101 RAX: ffffffffffffffda RBX: 00007ffc088e3368 RCX: 00007f00a703fd67 RDX: 0000000000000941 RSI: 00007ffc088e48d7 RDI: 00000000ffffff9c RBP: 00007ffc088e48d7 R08: 0000000000000001 R09: 0000000000000000 R10: 00000000000001b6 R11: 0000000000000246 R12: 0000000000000941 R13: 0000000000000000 R14: 00007ffc088e48d7 R15: 00007f00a7180040

Allocated by task 181: kasan_save_stack+0x2f/0x60 kasan_set_track+0x29/0x40 kasan_save_alloc_info+0x25/0x40 __kasan_kmalloc+0xc5/0xd0 __kmalloc+0x66/0x160 ecryptfs_generate_key_packet_set+0x6d2/0xde0 ecryptfs_write_metadata+0x30a/0x550 ecryptfs_initialize_file+0x77/0x150 ecryptfs_create+0x1c2/0x2f0 path_openat+0x17cf/0x1ba0 do_filp_open+0x15e/0x290 do_sys_openat2+0x122/0x160 __x64_sys_openat+0xef/0x170 do_syscall_64+0x60/0xd0 entry_SYSCALL_64_after_hwframe+0x6e/0xd8

Weakness

The product writes data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

• For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer.

• Be wary that a language’s interface to native code may still be subject to overflows, even if the language itself is theoretically safe.

• Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

• Examples include the Safe C String Library (SafeStr) by Messier and Viega [REF-57], and the Strsafe.h library from Microsoft [REF-56]. These libraries provide safer versions of overflow-prone string-handling functions.

• Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking.

• D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] discusses canary-based detection in detail.

• Consider adhering to the following rules when allocating and managing an application’s memory:

• Run or compile the software using features or extensions that randomly arrange the positions of a program’s executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code.

• Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as “rebasing” (for Windows) and “prelinking” (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking.

• For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].

• Use a CPU and operating system that offers Data Execution Protection (using hardware NX or XD bits) or the equivalent techniques that simulate this feature in software, such as PaX [REF-60] [REF-61]. These techniques ensure that any instruction executed is exclusively at a memory address that is part of the code segment.

• For more information on these techniques see D3-PSEP (Process Segment Execution Prevention) from D3FEND [REF-1336].

References

• https://git.kernel.org/stable/c/0d0f8ba042af16519f1ef7dd10463a33b21b677c
• https://git.kernel.org/stable/c/12db25a54ce6bb22b0af28010fff53ef9cb3fe93
• https://git.kernel.org/stable/c/1c125b9287e58f364d82174efb167414b92b11f1
• https://git.kernel.org/stable/c/235b85981051cd68fc215fd32a81c6f116bfc4df
• https://git.kernel.org/stable/c/2ed750b7ae1b5dc72896d7dd114c419afd3d1910
• https://git.kernel.org/stable/c/85a6a1aff08ec9f5b929d345d066e2830e8818e5
• https://git.kernel.org/stable/c/a20f09452e2f58f761d11ad7b96b5c894c91030e
• https://git.kernel.org/stable/c/edbfc42ab080e78c6907d40a42c9d10b69e445c1
• https://git.kernel.org/stable/c/f6008487f1eeb8693f8d2a36a89c87d9122ddf74
• https://git.kernel.org/stable/c/0d0f8ba042af16519f1ef7dd10463a33b21b677c
• https://git.kernel.org/stable/c/12db25a54ce6bb22b0af28010fff53ef9cb3fe93
• https://git.kernel.org/stable/c/1c125b9287e58f364d82174efb167414b92b11f1
• https://git.kernel.org/stable/c/235b85981051cd68fc215fd32a81c6f116bfc4df
• https://git.kernel.org/stable/c/2ed750b7ae1b5dc72896d7dd114c419afd3d1910
• https://git.kernel.org/stable/c/85a6a1aff08ec9f5b929d345d066e2830e8818e5
• https://git.kernel.org/stable/c/a20f09452e2f58f761d11ad7b96b5c894c91030e
• https://git.kernel.org/stable/c/edbfc42ab080e78c6907d40a42c9d10b69e445c1
• https://git.kernel.org/stable/c/f6008487f1eeb8693f8d2a36a89c87d9122ddf74