gen_init_cpio.c: fix buffer allocation size #5
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Fix potential buffer overflow by allocating space for null terminator in hardlink name buffer.
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Here's the issue I found: |
ptr1337
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[ Upstream commit ee684de ] As shown in [1], it is possible to corrupt a BPF ELF file such that arbitrary BPF instructions are loaded by libbpf. This can be done by setting a symbol (BPF program) section offset to a large (unsigned) number such that <section start + symbol offset> overflows and points before the section data in the memory. Consider the situation below where: - prog_start = sec_start + symbol_offset <-- size_t overflow here - prog_end = prog_start + prog_size prog_start sec_start prog_end sec_end | | | | v v v v .....................|################################|............ The report in [1] also provides a corrupted BPF ELF which can be used as a reproducer: $ readelf -S crash Section Headers: [Nr] Name Type Address Offset Size EntSize Flags Link Info Align ... [ 2] uretprobe.mu[...] PROGBITS 0000000000000000 00000040 0000000000000068 0000000000000000 AX 0 0 8 $ readelf -s crash Symbol table '.symtab' contains 8 entries: Num: Value Size Type Bind Vis Ndx Name ... 6: ffffffffffffffb8 104 FUNC GLOBAL DEFAULT 2 handle_tp Here, the handle_tp prog has section offset ffffffffffffffb8, i.e. will point before the actual memory where section 2 is allocated. This is also reported by AddressSanitizer: ================================================================= ==1232==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x7c7302fe0000 at pc 0x7fc3046e4b77 bp 0x7ffe64677cd0 sp 0x7ffe64677490 READ of size 104 at 0x7c7302fe0000 thread T0 #0 0x7fc3046e4b76 in memcpy (/lib64/libasan.so.8+0xe4b76) #1 0x00000040df3e in bpf_object__init_prog /src/libbpf/src/libbpf.c:856 #2 0x00000040df3e in bpf_object__add_programs /src/libbpf/src/libbpf.c:928 #3 0x00000040df3e in bpf_object__elf_collect /src/libbpf/src/libbpf.c:3930 #4 0x00000040df3e in bpf_object_open /src/libbpf/src/libbpf.c:8067 #5 0x00000040f176 in bpf_object__open_file /src/libbpf/src/libbpf.c:8090 #6 0x000000400c16 in main /poc/poc.c:8 torvalds#7 0x7fc3043d25b4 in __libc_start_call_main (/lib64/libc.so.6+0x35b4) torvalds#8 0x7fc3043d2667 in __libc_start_main@@GLIBC_2.34 (/lib64/libc.so.6+0x3667) torvalds#9 0x000000400b34 in _start (/poc/poc+0x400b34) 0x7c7302fe0000 is located 64 bytes before 104-byte region [0x7c7302fe0040,0x7c7302fe00a8) allocated by thread T0 here: #0 0x7fc3046e716b in malloc (/lib64/libasan.so.8+0xe716b) #1 0x7fc3045ee600 in __libelf_set_rawdata_wrlock (/lib64/libelf.so.1+0xb600) #2 0x7fc3045ef018 in __elf_getdata_rdlock (/lib64/libelf.so.1+0xc018) #3 0x00000040642f in elf_sec_data /src/libbpf/src/libbpf.c:3740 The problem here is that currently, libbpf only checks that the program end is within the section bounds. There used to be a check `while (sec_off < sec_sz)` in bpf_object__add_programs, however, it was removed by commit 6245947 ("libbpf: Allow gaps in BPF program sections to support overriden weak functions"). Add a check for detecting the overflow of `sec_off + prog_sz` to bpf_object__init_prog to fix this issue. [1] https://github.com/lmarch2/poc/blob/main/libbpf/libbpf.md Fixes: 6245947 ("libbpf: Allow gaps in BPF program sections to support overriden weak functions") Reported-by: lmarch2 <[email protected]> Signed-off-by: Viktor Malik <[email protected]> Signed-off-by: Andrii Nakryiko <[email protected]> Reviewed-by: Shung-Hsi Yu <[email protected]> Link: https://github.com/lmarch2/poc/blob/main/libbpf/libbpf.md Link: https://lore.kernel.org/bpf/[email protected] Signed-off-by: Sasha Levin <[email protected]>
ptr1337
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Jun 19, 2025
commit c98cc97 upstream. Running a modified trace-cmd record --nosplice where it does a mmap of the ring buffer when '--nosplice' is set, caused the following lockdep splat: ====================================================== WARNING: possible circular locking dependency detected 6.15.0-rc7-test-00002-gfb7d03d8a82f torvalds#551 Not tainted ------------------------------------------------------ trace-cmd/1113 is trying to acquire lock: ffff888100062888 (&buffer->mutex){+.+.}-{4:4}, at: ring_buffer_map+0x11c/0xe70 but task is already holding lock: ffff888100a5f9f8 (&cpu_buffer->mapping_lock){+.+.}-{4:4}, at: ring_buffer_map+0xcf/0xe70 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #5 (&cpu_buffer->mapping_lock){+.+.}-{4:4}: __mutex_lock+0x192/0x18c0 ring_buffer_map+0xcf/0xe70 tracing_buffers_mmap+0x1c4/0x3b0 __mmap_region+0xd8d/0x1f70 do_mmap+0x9d7/0x1010 vm_mmap_pgoff+0x20b/0x390 ksys_mmap_pgoff+0x2e9/0x440 do_syscall_64+0x79/0x1c0 entry_SYSCALL_64_after_hwframe+0x76/0x7e -> #4 (&mm->mmap_lock){++++}-{4:4}: __might_fault+0xa5/0x110 _copy_to_user+0x22/0x80 _perf_ioctl+0x61b/0x1b70 perf_ioctl+0x62/0x90 __x64_sys_ioctl+0x134/0x190 do_syscall_64+0x79/0x1c0 entry_SYSCALL_64_after_hwframe+0x76/0x7e -> #3 (&cpuctx_mutex){+.+.}-{4:4}: __mutex_lock+0x192/0x18c0 perf_event_init_cpu+0x325/0x7c0 perf_event_init+0x52a/0x5b0 start_kernel+0x263/0x3e0 x86_64_start_reservations+0x24/0x30 x86_64_start_kernel+0x95/0xa0 common_startup_64+0x13e/0x141 -> #2 (pmus_lock){+.+.}-{4:4}: __mutex_lock+0x192/0x18c0 perf_event_init_cpu+0xb7/0x7c0 cpuhp_invoke_callback+0x2c0/0x1030 __cpuhp_invoke_callback_range+0xbf/0x1f0 _cpu_up+0x2e7/0x690 cpu_up+0x117/0x170 cpuhp_bringup_mask+0xd5/0x120 bringup_nonboot_cpus+0x13d/0x170 smp_init+0x2b/0xf0 kernel_init_freeable+0x441/0x6d0 kernel_init+0x1e/0x160 ret_from_fork+0x34/0x70 ret_from_fork_asm+0x1a/0x30 -> #1 (cpu_hotplug_lock){++++}-{0:0}: cpus_read_lock+0x2a/0xd0 ring_buffer_resize+0x610/0x14e0 __tracing_resize_ring_buffer.part.0+0x42/0x120 tracing_set_tracer+0x7bd/0xa80 tracing_set_trace_write+0x132/0x1e0 vfs_write+0x21c/0xe80 ksys_write+0xf9/0x1c0 do_syscall_64+0x79/0x1c0 entry_SYSCALL_64_after_hwframe+0x76/0x7e -> #0 (&buffer->mutex){+.+.}-{4:4}: __lock_acquire+0x1405/0x2210 lock_acquire+0x174/0x310 __mutex_lock+0x192/0x18c0 ring_buffer_map+0x11c/0xe70 tracing_buffers_mmap+0x1c4/0x3b0 __mmap_region+0xd8d/0x1f70 do_mmap+0x9d7/0x1010 vm_mmap_pgoff+0x20b/0x390 ksys_mmap_pgoff+0x2e9/0x440 do_syscall_64+0x79/0x1c0 entry_SYSCALL_64_after_hwframe+0x76/0x7e other info that might help us debug this: Chain exists of: &buffer->mutex --> &mm->mmap_lock --> &cpu_buffer->mapping_lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&cpu_buffer->mapping_lock); lock(&mm->mmap_lock); lock(&cpu_buffer->mapping_lock); lock(&buffer->mutex); *** DEADLOCK *** 2 locks held by trace-cmd/1113: #0: ffff888106b847e0 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x192/0x390 #1: ffff888100a5f9f8 (&cpu_buffer->mapping_lock){+.+.}-{4:4}, at: ring_buffer_map+0xcf/0xe70 stack backtrace: CPU: 5 UID: 0 PID: 1113 Comm: trace-cmd Not tainted 6.15.0-rc7-test-00002-gfb7d03d8a82f torvalds#551 PREEMPT Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Call Trace: <TASK> dump_stack_lvl+0x6e/0xa0 print_circular_bug.cold+0x178/0x1be check_noncircular+0x146/0x160 __lock_acquire+0x1405/0x2210 lock_acquire+0x174/0x310 ? ring_buffer_map+0x11c/0xe70 ? ring_buffer_map+0x11c/0xe70 ? __mutex_lock+0x169/0x18c0 __mutex_lock+0x192/0x18c0 ? ring_buffer_map+0x11c/0xe70 ? ring_buffer_map+0x11c/0xe70 ? function_trace_call+0x296/0x370 ? __pfx___mutex_lock+0x10/0x10 ? __pfx_function_trace_call+0x10/0x10 ? __pfx___mutex_lock+0x10/0x10 ? _raw_spin_unlock+0x2d/0x50 ? ring_buffer_map+0x11c/0xe70 ? ring_buffer_map+0x11c/0xe70 ? __mutex_lock+0x5/0x18c0 ring_buffer_map+0x11c/0xe70 ? do_raw_spin_lock+0x12d/0x270 ? find_held_lock+0x2b/0x80 ? _raw_spin_unlock+0x2d/0x50 ? rcu_is_watching+0x15/0xb0 ? _raw_spin_unlock+0x2d/0x50 ? trace_preempt_on+0xd0/0x110 tracing_buffers_mmap+0x1c4/0x3b0 __mmap_region+0xd8d/0x1f70 ? ring_buffer_lock_reserve+0x99/0xff0 ? __pfx___mmap_region+0x10/0x10 ? ring_buffer_lock_reserve+0x99/0xff0 ? __pfx_ring_buffer_lock_reserve+0x10/0x10 ? __pfx_ring_buffer_lock_reserve+0x10/0x10 ? bpf_lsm_mmap_addr+0x4/0x10 ? security_mmap_addr+0x46/0xd0 ? lock_is_held_type+0xd9/0x130 do_mmap+0x9d7/0x1010 ? 0xffffffffc0370095 ? __pfx_do_mmap+0x10/0x10 vm_mmap_pgoff+0x20b/0x390 ? __pfx_vm_mmap_pgoff+0x10/0x10 ? 0xffffffffc0370095 ksys_mmap_pgoff+0x2e9/0x440 do_syscall_64+0x79/0x1c0 entry_SYSCALL_64_after_hwframe+0x76/0x7e RIP: 0033:0x7fb0963a7de2 Code: 00 00 00 0f 1f 44 00 00 41 f7 c1 ff 0f 00 00 75 27 55 89 cd 53 48 89 fb 48 85 ff 74 3b 41 89 ea 48 89 df b8 09 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 76 5b 5d c3 0f 1f 00 48 8b 05 e1 9f 0d 00 64 RSP: 002b:00007ffdcc8fb878 EFLAGS: 00000246 ORIG_RAX: 0000000000000009 RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fb0963a7de2 RDX: 0000000000000001 RSI: 0000000000001000 RDI: 0000000000000000 RBP: 0000000000000001 R08: 0000000000000006 R09: 0000000000000000 R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000 R13: 00007ffdcc8fbe68 R14: 00007fb096628000 R15: 00005633e01a5c90 </TASK> The issue is that cpus_read_lock() is taken within buffer->mutex. The memory mapped pages are taken with the mmap_lock held. The buffer->mutex is taken within the cpu_buffer->mapping_lock. There's quite a chain with all these locks, where the deadlock can be fixed by moving the cpus_read_lock() outside the taking of the buffer->mutex. Cc: [email protected] Cc: Masami Hiramatsu <[email protected]> Cc: Mathieu Desnoyers <[email protected]> Cc: Vincent Donnefort <[email protected]> Link: https://lore.kernel.org/[email protected] Fixes: 117c392 ("ring-buffer: Introducing ring-buffer mapping functions") Signed-off-by: Steven Rostedt (Google) <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]>
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Fix potential buffer overflow by allocating space for null terminator in hardlink name buffer.