When parsing a share-root relative native symlink, memcpy copies smb_target+1 (skipping the leading separator) but uses strlen(smb_target)+1 as the length, reading one byte past the allocated buffer. This fixes the following KASAN splat when accessing an SMB symlink with a target of '\a\b': BUG: KASAN: slab-out-of-bounds in smb2_parse_native_symlink+0x4f5/0xca0 Read of size 5 at addr ffff88800878fe21 by task netfsfuzz-execu/1 CPU: 1 UID: 0 PID: 1 Comm: netfsfuzz-execu Tainted: G N 7.2.0-11943-g2709dd5ae32f-dirty #1 PREEMPT(lazy) Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996) Call Trace: <TASK> dump_stack_lvl+0x7b/0xa0 print_report+0xd0/0x630 kasan_report+0xe5/0x120 kasan_check_range+0x105/0x1b0 __asan_memcpy+0x23/0x60 smb2_parse_native_symlink+0x4f5/0xca0 parse_reparse_point+0x68a/0x1530 reparse_info_to_fattr+0x752/0xa20 cifs_get_fattr+0x873/0x15b0 cifs_get_inode_info+0xc0/0x310 cifs_lookup+0x308/0xa70 __lookup_slow+0x122/0x2b0 lookup_slow+0x50/0x70 path_lookupat+0x525/0xaf0 filename_lookup+0x1f2/0x550 vfs_statx+0xd1/0x1a0 vfs_fstatat+0x65/0xc0 __do_sys_newfstatat+0x9a/0x120 do_syscall_64+0xdd/0x4a0 entry_SYSCALL_64_after_hwframe+0x77/0x7f
Unified · Split
| @@ -971,7 +971,8 @@ globalroot: · 970 unmodified lines | |||
| 971 | linux_target[i*3 + 1] = '.'; | 971 | linux_target[i*3 + 1] = '.'; |
| 972 | linux_target[i*3 + 2] = sep; | 972 | linux_target[i*3 + 2] = sep; |
| 973 | } | 973 | } |
| 974 | memcpy(linux_target + levels*3, smb_target+1, smb_target_len); /* +1 to skip leading sep */ | 974 | /* +1 to skip leading sep */ |
| 975 | memcpy(linux_target + levels*3, smb_target+1, smb_target_len-1); | ||
| 975 | } else { | 976 | } else { |
| 976 | /* | 977 | /* |
| 977 | * This is either an absolute symlink in POSIX-style format | 978 | * This is either an absolute symlink in POSIX-style format |