4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Vincent Pelletier plr.vincent@gmail.com
commit 1816494330a83f2a064499d8ed2797045641f92c upstream.
This change has the following effects, in order of descreasing importance:
1) Prevent a stack buffer overflow
2) Do not append an unnecessary NULL to an anyway binary buffer, which is writing one byte past client_digest when caller is: chap_string_to_hex(client_digest, chap_r, strlen(chap_r));
The latter was found by KASAN (see below) when input value hes expected size (32 hex chars), and further analysis revealed a stack buffer overflow can happen when network-received value is longer, allowing an unauthenticated remote attacker to smash up to 17 bytes after destination buffer (16 bytes attacker-controlled and one null). As switching to hex2bin requires specifying destination buffer length, and does not internally append any null, it solves both issues.
This addresses CVE-2018-14633.
Beyond this:
- Validate received value length and check hex2bin accepted the input, to log this rejection reason instead of just failing authentication.
- Only log received CHAP_R and CHAP_C values once they passed sanity checks.
================================================================== BUG: KASAN: stack-out-of-bounds in chap_string_to_hex+0x32/0x60 [iscsi_target_mod] Write of size 1 at addr ffff8801090ef7c8 by task kworker/0:0/1021
CPU: 0 PID: 1021 Comm: kworker/0:0 Tainted: G O 4.17.8kasan.sess.connops+ #2 Hardware name: To be filled by O.E.M. To be filled by O.E.M./Aptio CRB, BIOS 5.6.5 05/19/2014 Workqueue: events iscsi_target_do_login_rx [iscsi_target_mod] Call Trace: dump_stack+0x71/0xac print_address_description+0x65/0x22e ? chap_string_to_hex+0x32/0x60 [iscsi_target_mod] kasan_report.cold.6+0x241/0x2fd chap_string_to_hex+0x32/0x60 [iscsi_target_mod] chap_server_compute_md5.isra.2+0x2cb/0x860 [iscsi_target_mod] ? chap_binaryhex_to_asciihex.constprop.5+0x50/0x50 [iscsi_target_mod] ? ftrace_caller_op_ptr+0xe/0xe ? __orc_find+0x6f/0xc0 ? unwind_next_frame+0x231/0x850 ? kthread+0x1a0/0x1c0 ? ret_from_fork+0x35/0x40 ? ret_from_fork+0x35/0x40 ? iscsi_target_do_login_rx+0x3bc/0x4c0 [iscsi_target_mod] ? deref_stack_reg+0xd0/0xd0 ? iscsi_target_do_login_rx+0x3bc/0x4c0 [iscsi_target_mod] ? is_module_text_address+0xa/0x11 ? kernel_text_address+0x4c/0x110 ? __save_stack_trace+0x82/0x100 ? ret_from_fork+0x35/0x40 ? save_stack+0x8c/0xb0 ? 0xffffffffc1660000 ? iscsi_target_do_login+0x155/0x8d0 [iscsi_target_mod] ? iscsi_target_do_login_rx+0x3bc/0x4c0 [iscsi_target_mod] ? process_one_work+0x35c/0x640 ? worker_thread+0x66/0x5d0 ? kthread+0x1a0/0x1c0 ? ret_from_fork+0x35/0x40 ? iscsi_update_param_value+0x80/0x80 [iscsi_target_mod] ? iscsit_release_cmd+0x170/0x170 [iscsi_target_mod] chap_main_loop+0x172/0x570 [iscsi_target_mod] ? chap_server_compute_md5.isra.2+0x860/0x860 [iscsi_target_mod] ? rx_data+0xd6/0x120 [iscsi_target_mod] ? iscsit_print_session_params+0xd0/0xd0 [iscsi_target_mod] ? cyc2ns_read_begin.part.2+0x90/0x90 ? _raw_spin_lock_irqsave+0x25/0x50 ? memcmp+0x45/0x70 iscsi_target_do_login+0x875/0x8d0 [iscsi_target_mod] ? iscsi_target_check_first_request.isra.5+0x1a0/0x1a0 [iscsi_target_mod] ? del_timer+0xe0/0xe0 ? memset+0x1f/0x40 ? flush_sigqueue+0x29/0xd0 iscsi_target_do_login_rx+0x3bc/0x4c0 [iscsi_target_mod] ? iscsi_target_nego_release+0x80/0x80 [iscsi_target_mod] ? iscsi_target_restore_sock_callbacks+0x130/0x130 [iscsi_target_mod] process_one_work+0x35c/0x640 worker_thread+0x66/0x5d0 ? flush_rcu_work+0x40/0x40 kthread+0x1a0/0x1c0 ? kthread_bind+0x30/0x30 ret_from_fork+0x35/0x40
The buggy address belongs to the page: page:ffffea0004243bc0 count:0 mapcount:0 mapping:0000000000000000 index:0x0 flags: 0x17fffc000000000() raw: 017fffc000000000 0000000000000000 0000000000000000 00000000ffffffff raw: ffffea0004243c20 ffffea0004243ba0 0000000000000000 0000000000000000 page dumped because: kasan: bad access detected
Memory state around the buggy address: ffff8801090ef680: f2 f2 f2 f2 f2 f2 f2 01 f2 f2 f2 f2 f2 f2 f2 00 ffff8801090ef700: f2 f2 f2 f2 f2 f2 f2 00 02 f2 f2 f2 f2 f2 f2 00
ffff8801090ef780: 00 f2 f2 f2 f2 f2 f2 00 00 f2 f2 f2 f2 f2 f2 00
^ ffff8801090ef800: 00 f2 f2 f2 f2 f2 f2 00 00 00 00 02 f2 f2 f2 f2 ffff8801090ef880: f2 f2 f2 00 00 00 00 00 00 00 00 f2 f2 f2 f2 00 ==================================================================
Signed-off-by: Vincent Pelletier plr.vincent@gmail.com Reviewed-by: Mike Christie mchristi@redhat.com Signed-off-by: Martin K. Petersen martin.petersen@oracle.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/target/iscsi/iscsi_target_auth.c | 30 ++++++++++++++---------------- 1 file changed, 14 insertions(+), 16 deletions(-)
--- a/drivers/target/iscsi/iscsi_target_auth.c +++ b/drivers/target/iscsi/iscsi_target_auth.c @@ -26,18 +26,6 @@ #include "iscsi_target_nego.h" #include "iscsi_target_auth.h"
-static int chap_string_to_hex(unsigned char *dst, unsigned char *src, int len) -{ - int j = DIV_ROUND_UP(len, 2), rc; - - rc = hex2bin(dst, src, j); - if (rc < 0) - pr_debug("CHAP string contains non hex digit symbols\n"); - - dst[j] = '\0'; - return j; -} - static void chap_binaryhex_to_asciihex(char *dst, char *src, int src_len) { int i; @@ -240,9 +228,16 @@ static int chap_server_compute_md5( pr_err("Could not find CHAP_R.\n"); goto out; } + if (strlen(chap_r) != MD5_SIGNATURE_SIZE * 2) { + pr_err("Malformed CHAP_R\n"); + goto out; + } + if (hex2bin(client_digest, chap_r, MD5_SIGNATURE_SIZE) < 0) { + pr_err("Malformed CHAP_R\n"); + goto out; + }
pr_debug("[server] Got CHAP_R=%s\n", chap_r); - chap_string_to_hex(client_digest, chap_r, strlen(chap_r));
tfm = crypto_alloc_shash("md5", 0, 0); if (IS_ERR(tfm)) { @@ -341,9 +336,7 @@ static int chap_server_compute_md5( pr_err("Could not find CHAP_C.\n"); goto out; } - pr_debug("[server] Got CHAP_C=%s\n", challenge); - challenge_len = chap_string_to_hex(challenge_binhex, challenge, - strlen(challenge)); + challenge_len = DIV_ROUND_UP(strlen(challenge), 2); if (!challenge_len) { pr_err("Unable to convert incoming challenge\n"); goto out; @@ -352,6 +345,11 @@ static int chap_server_compute_md5( pr_err("CHAP_C exceeds maximum binary size of 1024 bytes\n"); goto out; } + if (hex2bin(challenge_binhex, challenge, challenge_len) < 0) { + pr_err("Malformed CHAP_C\n"); + goto out; + } + pr_debug("[server] Got CHAP_C=%s\n", challenge); /* * During mutual authentication, the CHAP_C generated by the * initiator must not match the original CHAP_C generated by