CVE-2025-37785

En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: ext4: corrección de lectura OOB al comprobar el directorio dotdot Montar un sistema de archivos dañado con un directorio que contiene una entrada de directorio '.' con rec_len == tamaño de bloque da como resultado una lectura fuera de los límites (más adelante, cuando se elimina el directorio dañado). ext4_empty_dir() asume que cada directorio ext4 contiene al menos '.' y '..' como entradas de directorio en el primer bloque de datos. Primero carga la entrada de directorio '.', realiza comprobaciones de cordura llamando a ext4_check_dir_entry() y luego usa su miembro rec_len para calcular la ubicación de la entrada de directorio '..' (en ext4_next_entry). Asume que la entrada de directorio '..' encaja en el mismo bloque de datos. Si el rec_len de '.' Si es exactamente un bloque (4 KB), no cumple con las comprobaciones de seguridad (se considera la última entrada de directorio del bloque de datos) y deja el puntero "struct ext4_dir_entry_2 *de" justo después de la ranura de memoria asignada al bloque de datos. La siguiente llamada a ext4_check_dir_entry() con el nuevo valor de de desreferencia este puntero, lo que resulta en un acceso a la memoria fuera de los límites. Para solucionar esto, extienda __ext4_check_dir_entry() para verificar las entradas de directorio "." que llegan al final del bloque de datos. Asegúrese de ignorar las entradas de directorio falsas para la suma de comprobación (verificando name_len para ver si es distinto de cero). Nota: KASAN informa que esto es un use-after-free en caso de que otra estructura se haya liberado recientemente de la ranura más allá del límite, pero en realidad es una lectura fuera de banda (OOB). Este problema fue detectado por la herramienta syzkaller. Rastreo de llamadas: [38.594108] ERROR: KASAN: slab-use-after-free in __ext4_check_dir_entry+0x67e/0x710 [ 38.594649] Read of size 2 at addr ffff88802b41a004 by task syz-executor/5375 [ 38.595158] [ 38.595288] CPU: 0 UID: 0 PID: 5375 Comm: syz-executor Not tainted 6.14.0-rc7 #1 [ 38.595298] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 [ 38.595304] Call Trace: [ 38.595308] [ 38.595311] dump_stack_lvl+0xa7/0xd0 [ 38.595325] print_address_description.constprop.0+0x2c/0x3f0 [ 38.595339] ? __ext4_check_dir_entry+0x67e/0x710 [ 38.595349] print_report+0xaa/0x250 [ 38.595359] ? __ext4_check_dir_entry+0x67e/0x710 [ 38.595368] ? kasan_addr_to_slab+0x9/0x90 [ 38.595378] kasan_report+0xab/0xe0 [ 38.595389] ? __ext4_check_dir_entry+0x67e/0x710 [ 38.595400] __ext4_check_dir_entry+0x67e/0x710 [ 38.595410] ext4_empty_dir+0x465/0x990 [ 38.595421] ? __pfx_ext4_empty_dir+0x10/0x10 [ 38.595432] ext4_rmdir.part.0+0x29a/0xd10 [ 38.595441] ? __dquot_initialize+0x2a7/0xbf0 [ 38.595455] ? __pfx_ext4_rmdir.part.0+0x10/0x10 [ 38.595464] ? __pfx___dquot_initialize+0x10/0x10 [ 38.595478] ? down_write+0xdb/0x140 [ 38.595487] ? __pfx_down_write+0x10/0x10 [ 38.595497] ext4_rmdir+0xee/0x140 [ 38.595506] vfs_rmdir+0x209/0x670 [ 38.595517] ? lookup_one_qstr_excl+0x3b/0x190 [ 38.595529] do_rmdir+0x363/0x3c0 [ 38.595537] ? __pfx_do_rmdir+0x10/0x10 [ 38.595544] ? strncpy_from_user+0x1ff/0x2e0 [ 38.595561] __x64_sys_unlinkat+0xf0/0x130 [ 38.595570] do_syscall_64+0x5b/0x180 [ 38.595583] entry_SYSCALL_64_after_hwframe+0x76/0x7e

In the Linux kernel, the following vulnerability has been resolved: ext4: fix OOB read when checking dotdot dir Mounting a corrupted filesystem with directory which contains '.' dir entry with rec_len == block size results in out-of-bounds read (later on, when the corrupted directory is removed). ext4_empty_dir() assumes every ext4 directory contains at least '.' and '..' as directory entries in the first data block. It first loads the '.' dir entry, performs sanity checks by calling ext4_check_dir_entry() and then uses its rec_len member to compute the location of '..' dir entry (in ext4_next_entry). It assumes the '..' dir entry fits into the same data block. If the rec_len of '.' is precisely one block (4KB), it slips through the sanity checks (it is considered the last directory entry in the data block) and leaves "struct ext4_dir_entry_2 *de" point exactly past the memory slot allocated to the data block. The following call to ext4_check_dir_entry() on new value of de then dereferences this pointer which results in out-of-bounds mem access. Fix this by extending __ext4_check_dir_entry() to check for '.' dir entries that reach the end of data block. Make sure to ignore the phony dir entries for checksum (by checking name_len for non-zero). Note: This is reported by KASAN as use-after-free in case another structure was recently freed from the slot past the bound, but it is really an OOB read. This issue was found by syzkaller tool. Call Trace: [ 38.594108] BUG: KASAN: slab-use-after-free in __ext4_check_dir_entry+0x67e/0x710 [ 38.594649] Read of size 2 at addr ffff88802b41a004 by task syz-executor/5375 [ 38.595158] [ 38.595288] CPU: 0 UID: 0 PID: 5375 Comm: syz-executor Not tainted 6.14.0-rc7 #1 [ 38.595298] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 [ 38.595304] Call Trace: [ 38.595308] <TASK> [ 38.595311] dump_stack_lvl+0xa7/0xd0 [ 38.595325] print_address_description.constprop.0+0x2c/0x3f0 [ 38.595339] ? __ext4_check_dir_entry+0x67e/0x710 [ 38.595349] print_report+0xaa/0x250 [ 38.595359] ? __ext4_check_dir_entry+0x67e/0x710 [ 38.595368] ? kasan_addr_to_slab+0x9/0x90 [ 38.595378] kasan_report+0xab/0xe0 [ 38.595389] ? __ext4_check_dir_entry+0x67e/0x710 [ 38.595400] __ext4_check_dir_entry+0x67e/0x710 [ 38.595410] ext4_empty_dir+0x465/0x990 [ 38.595421] ? __pfx_ext4_empty_dir+0x10/0x10 [ 38.595432] ext4_rmdir.part.0+0x29a/0xd10 [ 38.595441] ? __dquot_initialize+0x2a7/0xbf0 [ 38.595455] ? __pfx_ext4_rmdir.part.0+0x10/0x10 [ 38.595464] ? __pfx___dquot_initialize+0x10/0x10 [ 38.595478] ? down_write+0xdb/0x140 [ 38.595487] ? __pfx_down_write+0x10/0x10 [ 38.595497] ext4_rmdir+0xee/0x140 [ 38.595506] vfs_rmdir+0x209/0x670 [ 38.595517] ? lookup_one_qstr_excl+0x3b/0x190 [ 38.595529] do_rmdir+0x363/0x3c0 [ 38.595537] ? __pfx_do_rmdir+0x10/0x10 [ 38.595544] ? strncpy_from_user+0x1ff/0x2e0 [ 38.595561] __x64_sys_unlinkat+0xf0/0x130 [ 38.595570] do_syscall_64+0x5b/0x180 [ 38.595583] entry_SYSCALL_64_after_hwframe+0x76/0x7e