The global QoS list 'qos_head' in net/atm/mpc.c is accessed from the /proc/net/atm/mpc procfs interface without proper synchronization. The read-side seq_file show path (mpc_show() -> atm_mpoa_disp_qos()) walks qos_head without any lock, while the write-side path (proc_mpc_write() -> parse_qos() -> atm_mpoa_delete_qos()) can unlink and kfree() entries immediately. Concurrent read/write therefore leads to a use-after-free.

Fix this by serializing all qos_head list operations with a mutex. A mutex is used because seq_printf() may sleep.

To avoid returning an unprotected pointer (and the resulting lifetime race), replace atm_mpoa_search_qos() with atm_mpoa_get_qos(), which copies the QoS under lock. Also add atm_mpoa_delete_qos_by_ip() so search+unlink+free is atomic under the same lock, preventing concurrent double-free/UAF scenarios.

KASAN report:

[ 15.911538] BUG: KASAN: slab-use-after-free in atm_mpoa_disp_qos+0x202/0x380 [ 15.911988] Read of size 8 at addr ffff888007517380 by task mpoa_uaf_poc/89 [ 15.912123] [ 15.912717] CPU: 0 UID: 0 PID: 89 Comm: mpoa_uaf_poc Not tainted 6.17.8 #1 PREEMPT(voluntary) [ 15.912950] Hardware name: QEMU Ubuntu 25.04 PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 [ 15.913110] Call Trace: [ 15.913167] <TASK> [ 15.913247] dump_stack_lvl+0x4e/0x70 [ 15.913343] ? atm_mpoa_disp_qos+0x202/0x380 [ 15.913364] print_report+0x174/0x4f6 [ 15.913386] ? __pfx__raw_spin_lock_irqsave+0x10/0x10 [ 15.913412] ? atm_mpoa_disp_qos+0x202/0x380 [ 15.913430] kasan_report+0xce/0x100 [ 15.913453] ? atm_mpoa_disp_qos+0x202/0x380 [ 15.913475] atm_mpoa_disp_qos+0x202/0x380 [ 15.913496] mpc_show+0x575/0x700 [ 15.913515] ? kasan_save_track+0x14/0x30 [ 15.913532] ? __pfx_mpc_show+0x10/0x10 [ 15.913550] ? __pfx_mutex_lock+0x10/0x10 [ 15.913565] ? seq_read_iter+0x697/0x1110 [ 15.913584] seq_read_iter+0x2bc/0x1110 [ 15.913607] seq_read+0x267/0x3d0 [ 15.913623] ? __pfx_seq_read+0x10/0x10 [ 15.913650] proc_reg_read+0x1ab/0x270 [ 15.913669] vfs_read+0x175/0xa10 [ 15.913687] ? do_sys_openat2+0x103/0x170 [ 15.913701] ? kmem_cache_free+0xc4/0x360 [ 15.913718] ? getname_flags.part.0+0xf3/0x470 [ 15.913734] ? __pfx_vfs_read+0x10/0x10 [ 15.913751] ? mutex_lock+0x81/0xe0 [ 15.913766] ? __pfx_mutex_lock+0x10/0x10 [ 15.913782] ? __rseq_handle_notify_resume+0x4c4/0xac0 [ 15.913802] ? fdget_pos+0x24d/0x4b0 [ 15.913829] ksys_read+0xf7/0x1c0 [ 15.913850] ? __pfx_ksys_read+0x10/0x10 [ 15.913877] do_syscall_64+0xa4/0x290 [ 15.913917] entry_SYSCALL_64_after_hwframe+0x77/0x7f [ 15.913981] RIP: 0033:0x45c982 [ 15.914171] Code: 08 0f 85 71 ea ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 f3 0f 1e fa 55 48 89 e5 [ 15.914239] RSP: 002b:00007f4b2b2cb0d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000 [ 15.914315] RAX: ffffffffffffffda RBX: 00007f4b2b2cc6c0 RCX: 000000000045c982 [ 15.914352] RDX: 0000000000000fff RSI: 00007f4b2b2cb220 RDI: 0000000000000014 [ 15.914382] RBP: 00007f4b2b2cb100 R08: 0000000000000000 R09: 0000000000000000 [ 15.914413] R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000000a [ 15.914445] R13: ffffffffffffffd0 R14: 0000000000000000 R15: 00007ffd386450c0 [ 15.914483] </TASK> [ 15.914533] [ 15.916812] Allocated by task 78: [ 15.916975] kasan_save_stack+0x30/0x50 [ 15.917047] kasan_save_track+0x14/0x30 [ 15.917105] __kasan_kmalloc+0x8f/0xa0 [ 15.917162] atm_mpoa_add_qos+0x1bb/0x3c0 [ 15.917220] parse_qos.cold+0x73/0x7d [ 15.917276] proc_mpc_write+0xf4/0x150 [ 15.917331] proc_reg_write+0x1ab/0x270 [ 15.917379] vfs_write+0x1ce/0xd30 [ 15.917431] ksys_write+0xf7/0x1c0 [ 15.917476] do_syscall_64+0xa4/0x290 [ 15.917523] entry_SYSCALL_64_after_hwframe+0x77/0x7f [ 15.917586] [ 15.917628] Freed by task 78: [ 15.917665] kasan_save_stack+0x30/0x50 [ 15.917714] kasan_save_track+0x14/0x30 [ 15.917762] kasan_save_free_info+0x3b/0x70 [ 15.917811] __kasan_slab_free+0x3e/0x50 [ 15.918058] kfree+0x121/0x340 [ 15.918135] atm_mpoa_delete_qos+0xad/0xd0 [ 15.918196] parse_qos+0x1e5/0x1f0 [ 15.918339] proc_mpc_write+0xf4/0x150 [ 15.918438] proc_reg_write+0x1ab/0x270 [ 15.918494] vfs_write+0x1ce/0xd30 [ 15.918538] ksys_write+0xf7/0x1c0 [ 15.918589] do_syscall_64+0xa4/0x290 [ 15.918634] entry_SYSCALL_64_after_hwframe+0x77/0x7f [ 15.918694] [ 15.918751] The buggy address belongs to the object at ffff888007517380 [ 15.918751] which belongs to the cache kmalloc-96 of size 96 [ 15.918911] The buggy address is located 0 bytes inside of [ 15.918911] freed 96-byte region [ffff888007517380, ffff8880075173e0) [ 15.919027] [ 15.919101] The buggy address belongs to the physical page: [ 15.919416] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888007517300 pfn:0x7517 [ 15.919679] anon flags: 0x100000000000000(node=0|zone=1) [ 15.920064] page_type: f5(slab) [ 15.920361] raw: 0100000000000000 ffff888006c41280 0000000000000000 dead000000000001 [ 15.920460] raw: ffff888007517300 0000000080200007 00000000f5000000 0000000000000000 [ 15.920577] page dumped because: kasan: bad access detected [ 15.920634] [ 15.920663] Memory state around the buggy address: [ 15.920860] ffff888007517280: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc [ 15.920944] ffff888007517300: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc [ 15.921017] >ffff888007517380: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc [ 15.921088] ^ [ 15.921163] ffff888007517400: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc [ 15.921222] ffff888007517480: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc

Reported-by: Minseong Kim ii4gsp@gmail.com Closes: https://lore.kernel.org/netdev/CAKrymDR1X3XTX_1ZW3XXXnuYH+kzsnv7Av5uivzR1sto... Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Minseong Kim ii4gsp@gmail.com --- net/atm/mpc.c | 184 ++++++++++++++++++++++++++++++++---------- net/atm/mpc.h | 3 +- net/atm/mpoa_caches.c | 17 ++-- net/atm/mpoa_proc.c | 2 +- 4 files changed, 149 insertions(+), 57 deletions(-)

diff --git a/net/atm/mpc.c b/net/atm/mpc.c index f6b447bba329..650081dd82d1 100644 --- a/net/atm/mpc.c +++ b/net/atm/mpc.c @@ -9,6 +9,7 @@ #include <linux/bitops.h> #include <linux/capability.h> #include <linux/seq_file.h> +#include <linux/mutex.h>

/* We are an ethernet device */ #include <linux/if_ether.h> @@ -122,6 +123,7 @@ static struct notifier_block mpoa_notifier = {

struct mpoa_client *mpcs = NULL; /* FIXME */ static struct atm_mpoa_qos *qos_head = NULL; +static DEFINE_MUTEX(qos_mutex); /* Protect qos_head list */ static DEFINE_TIMER(mpc_timer, mpc_cache_check);

@@ -172,67 +174,63 @@ static struct mpoa_client *find_mpc_by_lec(struct net_device *dev) */

/* - * Overwrites the old entry or makes a new one. + * Search for a QoS entry. Caller must hold qos_mutex. + * Returns pointer to entry if found, NULL otherwise. */ -struct atm_mpoa_qos *atm_mpoa_add_qos(__be32 dst_ip, struct atm_qos *qos) +static struct atm_mpoa_qos *__atm_mpoa_search_qos(__be32 dst_ip) { - struct atm_mpoa_qos *entry; - - entry = atm_mpoa_search_qos(dst_ip); - if (entry != NULL) { - entry->qos = *qos; - return entry; - } + struct atm_mpoa_qos *qos = qos_head;

- entry = kmalloc(sizeof(struct atm_mpoa_qos), GFP_KERNEL); - if (entry == NULL) { - pr_info("mpoa: out of memory\n"); - return entry; + while (qos) { + if (qos->ipaddr == dst_ip) + return qos; + qos = qos->next; } - - entry->ipaddr = dst_ip; - entry->qos = *qos; - - entry->next = qos_head; - qos_head = entry; - - return entry; + return NULL; }

-struct atm_mpoa_qos *atm_mpoa_search_qos(__be32 dst_ip) +/* + * Get a QoS entry by copying its value. + * Caller gets a COPY of qos under lock. + * Returns true if found and copied, false if not found. + * This avoids lifetime issues with the returned pointer. + */ +bool atm_mpoa_get_qos(__be32 dst_ip, struct atm_qos *out) { - struct atm_mpoa_qos *qos; + struct atm_mpoa_qos *q;

- qos = qos_head; - while (qos) { - if (qos->ipaddr == dst_ip) - break; - qos = qos->next; - } + if (!out) + return false;

- return qos; + mutex_lock(&qos_mutex); + q = __atm_mpoa_search_qos(dst_ip); + if (q) + *out = q->qos; + mutex_unlock(&qos_mutex); + + return q; }

/* - * Returns 0 for failure + * Delete a QoS entry from the list. Caller must hold qos_mutex. + * Returns 1 if found and deleted, 0 if not found. */ -int atm_mpoa_delete_qos(struct atm_mpoa_qos *entry) +static int __atm_mpoa_delete_qos_locked(struct atm_mpoa_qos *entry) { struct atm_mpoa_qos *curr;

- if (entry == NULL) + if (!entry) return 0; + if (entry == qos_head) { - qos_head = qos_head->next; - kfree(entry); + qos_head = entry->next; return 1; }

curr = qos_head; - while (curr != NULL) { + while (curr) { if (curr->next == entry) { curr->next = entry->next; - kfree(entry); return 1; } curr = curr->next; @@ -241,15 +239,107 @@ int atm_mpoa_delete_qos(struct atm_mpoa_qos *entry) return 0; }

+/* + * Delete a QoS entry by IP address. + * This is atomic: search+unlink+free happens entirely under lock, + * avoiding the double-free issue with atm_mpoa_delete_qos(atm_mpoa_search_qos(ipaddr)). + */ +int atm_mpoa_delete_qos_by_ip(__be32 dst_ip) +{ + struct atm_mpoa_qos *entry; + int ret = 0; + + mutex_lock(&qos_mutex); + entry = __atm_mpoa_search_qos(dst_ip); + if (entry) { + ret = __atm_mpoa_delete_qos_locked(entry); + if (ret) + kfree(entry); + } + mutex_unlock(&qos_mutex); + + return ret; +} + +/* + * Overwrites the old entry or makes a new one. + */ +struct atm_mpoa_qos *atm_mpoa_add_qos(__be32 dst_ip, struct atm_qos *qos) +{ + struct atm_mpoa_qos *entry; + struct atm_mpoa_qos *new; + + /* Fast path: update existing entry */ + mutex_lock(&qos_mutex); + entry = __atm_mpoa_search_qos(dst_ip); + if (entry) { + entry->qos = *qos; + mutex_unlock(&qos_mutex); + return entry; + } + mutex_unlock(&qos_mutex); + + /* Allocate outside lock */ + new = kmalloc(sizeof(*new), GFP_KERNEL); + if (!new) + return NULL; + + new->ipaddr = dst_ip; + new->qos = *qos; + + /* Re-check under lock to avoid duplicates */ + mutex_lock(&qos_mutex); + entry = __atm_mpoa_search_qos(dst_ip); + if (entry) { + entry->qos = *qos; + mutex_unlock(&qos_mutex); + kfree(new); + return entry; + } + + new->next = qos_head; + qos_head = new; + mutex_unlock(&qos_mutex); + + return new; +} + +/* + * Delete a QoS entry by pointer. + * WARNING: This function is unsafe if called with an entry pointer + * obtained outside of qos_mutex protection. The entry may have been + * freed by another thread between the time the pointer was obtained + * and when this function is called. + * Use atm_mpoa_delete_qos_by_ip() instead for safe deletion by IP address. + * Returns 0 for failure, 1 for success + */ +int atm_mpoa_delete_qos(struct atm_mpoa_qos *entry) +{ + int ret; + + if (!entry) + return 0; + + mutex_lock(&qos_mutex); + ret = __atm_mpoa_delete_qos_locked(entry); + if (ret) + kfree(entry); + mutex_unlock(&qos_mutex); + + return ret; +} + /* this is buggered - we need locking for qos_head */ void atm_mpoa_disp_qos(struct seq_file *m) { struct atm_mpoa_qos *qos;

- qos = qos_head; seq_printf(m, "QoS entries for shortcuts:\n"); - seq_printf(m, "IP address\n TX:max_pcr pcr min_pcr max_cdv max_sdu\n RX:max_pcr pcr min_pcr max_cdv max_sdu\n"); + seq_printf(m, "IP address\n TX:max_pcr pcr min_pcr max_cdv max_sdu\n" + " RX:max_pcr pcr min_pcr max_cdv max_sdu\n");

+ mutex_lock(&qos_mutex); + qos = qos_head; while (qos != NULL) { seq_printf(m, "%pI4\n %-7d %-7d %-7d %-7d %-7d\n %-7d %-7d %-7d %-7d %-7d\n", &qos->ipaddr, @@ -265,6 +355,7 @@ void atm_mpoa_disp_qos(struct seq_file *m) qos->qos.rxtp.max_sdu); qos = qos->next; } + mutex_unlock(&qos_mutex); }

static struct net_device *find_lec_by_itfnum(int itf) @@ -1118,13 +1209,16 @@ static void check_qos_and_open_shortcut(struct k_message *msg, in_cache_entry *entry) { __be32 dst_ip = msg->content.in_info.in_dst_ip; - struct atm_mpoa_qos *qos = atm_mpoa_search_qos(dst_ip); + struct atm_qos tmp_qos; + bool has_qos; eg_cache_entry *eg_entry = client->eg_ops->get_by_src_ip(dst_ip, client);

+ has_qos = atm_mpoa_get_qos(dst_ip, &tmp_qos); + if (eg_entry && eg_entry->shortcut) { if (eg_entry->shortcut->qos.txtp.traffic_class & msg->qos.txtp.traffic_class & - (qos ? qos->qos.txtp.traffic_class : ATM_UBR | ATM_CBR)) { + (has_qos ? tmp_qos.txtp.traffic_class : ATM_UBR | ATM_CBR)) { if (eg_entry->shortcut->qos.txtp.traffic_class == ATM_UBR) entry->shortcut = eg_entry->shortcut; else if (eg_entry->shortcut->qos.txtp.max_pcr > 0) @@ -1142,9 +1236,9 @@ static void check_qos_and_open_shortcut(struct k_message *msg,

/* No luck in the egress cache we must open an ingress SVC */ msg->type = OPEN_INGRESS_SVC; - if (qos && - (qos->qos.txtp.traffic_class == msg->qos.txtp.traffic_class)) { - msg->qos = qos->qos; + if (has_qos && + tmp_qos.txtp.traffic_class == msg->qos.txtp.traffic_class) { + msg->qos = tmp_qos; pr_info("(%s) trying to get a CBR shortcut\n", client->dev->name); } else @@ -1521,8 +1615,10 @@ static void __exit atm_mpoa_cleanup(void) mpc = tmp; }

+ mutex_lock(&qos_mutex); qos = qos_head; qos_head = NULL; + mutex_unlock(&qos_mutex); while (qos != NULL) { nextqos = qos->next; dprintk("freeing qos entry %p\n", qos); diff --git a/net/atm/mpc.h b/net/atm/mpc.h index 454abd07651a..0536946989ad 100644 --- a/net/atm/mpc.h +++ b/net/atm/mpc.h @@ -47,8 +47,9 @@ struct atm_mpoa_qos {

/* MPOA QoS operations */ struct atm_mpoa_qos *atm_mpoa_add_qos(__be32 dst_ip, struct atm_qos *qos); -struct atm_mpoa_qos *atm_mpoa_search_qos(__be32 dst_ip); +bool atm_mpoa_get_qos(__be32 dst_ip, struct atm_qos *out); int atm_mpoa_delete_qos(struct atm_mpoa_qos *qos); +int atm_mpoa_delete_qos_by_ip(__be32 dst_ip);

/* Display QoS entries. This is for the procfs */ struct seq_file; diff --git a/net/atm/mpoa_caches.c b/net/atm/mpoa_caches.c index f7a2f0e41105..30c5b10ee562 100644 --- a/net/atm/mpoa_caches.c +++ b/net/atm/mpoa_caches.c @@ -132,7 +132,6 @@ static in_cache_entry *in_cache_add_entry(__be32 dst_ip,

static int cache_hit(in_cache_entry *entry, struct mpoa_client *mpc) { - struct atm_mpoa_qos *qos; struct k_message msg;

entry->count++; @@ -144,9 +143,8 @@ static int cache_hit(in_cache_entry *entry, struct mpoa_client *mpc) msg.type = SND_MPOA_RES_RQST; msg.content.in_info = entry->ctrl_info; memcpy(msg.MPS_ctrl, mpc->mps_ctrl_addr, ATM_ESA_LEN); - qos = atm_mpoa_search_qos(entry->ctrl_info.in_dst_ip); - if (qos != NULL) - msg.qos = qos->qos; + if (!atm_mpoa_get_qos(entry->ctrl_info.in_dst_ip, &msg.qos)) + memset(&msg.qos, 0, sizeof(msg.qos)); msg_to_mpoad(&msg, mpc); entry->reply_wait = ktime_get_seconds(); entry->entry_state = INGRESS_RESOLVING; @@ -167,9 +165,8 @@ static int cache_hit(in_cache_entry *entry, struct mpoa_client *mpc) msg.type = SND_MPOA_RES_RQST; memcpy(msg.MPS_ctrl, mpc->mps_ctrl_addr, ATM_ESA_LEN); msg.content.in_info = entry->ctrl_info; - qos = atm_mpoa_search_qos(entry->ctrl_info.in_dst_ip); - if (qos != NULL) - msg.qos = qos->qos; + if (!atm_mpoa_get_qos(entry->ctrl_info.in_dst_ip, &msg.qos)) + memset(&msg.qos, 0, sizeof(msg.qos)); msg_to_mpoad(&msg, mpc); entry->reply_wait = ktime_get_seconds(); } @@ -249,7 +246,6 @@ static void clear_count_and_expired(struct mpoa_client *client) static void check_resolving_entries(struct mpoa_client *client) {

- struct atm_mpoa_qos *qos; in_cache_entry *entry; time64_t now; struct k_message msg; @@ -283,9 +279,8 @@ static void check_resolving_entries(struct mpoa_client *client) msg.type = SND_MPOA_RES_RTRY; memcpy(msg.MPS_ctrl, client->mps_ctrl_addr, ATM_ESA_LEN); msg.content.in_info = entry->ctrl_info; - qos = atm_mpoa_search_qos(entry->ctrl_info.in_dst_ip); - if (qos != NULL) - msg.qos = qos->qos; + if (!atm_mpoa_get_qos(entry->ctrl_info.in_dst_ip, &msg.qos)) + memset(&msg.qos, 0, sizeof(msg.qos)); msg_to_mpoad(&msg, client); entry->reply_wait = ktime_get_seconds(); } diff --git a/net/atm/mpoa_proc.c b/net/atm/mpoa_proc.c index aaf64b953915..600075c6022e 100644 --- a/net/atm/mpoa_proc.c +++ b/net/atm/mpoa_proc.c @@ -254,7 +254,7 @@ static int parse_qos(const char *buff) if (sscanf(buff, "del %hhu.%hhu.%hhu.%hhu", ip, ip+1, ip+2, ip+3) == 4) { ipaddr = *(__be32 *)ip; - return atm_mpoa_delete_qos(atm_mpoa_search_qos(ipaddr)); + return atm_mpoa_delete_qos_by_ip(ipaddr); }

if (sscanf(buff, "add %hhu.%hhu.%hhu.%hhu tx=%d,%d rx=tx",