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Re: [PATCH] scsi/qemu-pr-helper: Fix out-of-bounds access to trnptid_lis
From: |
Paolo Bonzini |
Subject: |
Re: [PATCH] scsi/qemu-pr-helper: Fix out-of-bounds access to trnptid_list[] |
Date: |
Mon, 16 Mar 2020 22:06:05 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 |
On 28/02/20 16:00, Christophe de Dinechin wrote:
> Compile error reported by gcc 10.0.1:
>
> scsi/qemu-pr-helper.c: In function ‘multipath_pr_out’:
> scsi/qemu-pr-helper.c:523:32: error: array subscript <unknown> is outside
> array bounds of ‘struct transportid *[0]’ [-Werror=array-bounds]
> 523 | paramp.trnptid_list[paramp.num_transportid++] = id;
> | ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
> In file included from scsi/qemu-pr-helper.c:36:
> /usr/include/mpath_persist.h:168:22: note: while referencing ‘trnptid_list’
> 168 | struct transportid *trnptid_list[];
> | ^~~~~~~~~~~~
> scsi/qemu-pr-helper.c:424:35: note: defined here ‘paramp’
> 424 | struct prout_param_descriptor paramp;
> | ^~~~~~
>
> This highlights an actual implementation issue in function multipath_pr_out.
> The variable paramp is declared with type `struct prout_param_descriptor`,
> which is a struct terminated by an empty array in mpath_persist.h:
>
> struct transportid *trnptid_list[];
>
> That empty array was filled with code that looked like that:
>
> trnptid_list[paramp.descr.num_transportid++] = id;
>
> This is an actual out-of-bounds access.
The fix unfortunately causes a compilation warning-turned-error because
of a flexible array member in the middle of a struct. The simplest fix
is just to malloc the struct:
diff --git a/scsi/qemu-pr-helper.c b/scsi/qemu-pr-helper.c
index 0101322..65a8261 100644
--- a/scsi/qemu-pr-helper.c
+++ b/scsi/qemu-pr-helper.c
@@ -421,15 +421,13 @@ static int multipath_pr_out(int fd, const uint8_t *cdb,
uint8_t *sense,
int rq_servact = cdb[1];
int rq_scope = cdb[2] >> 4;
int rq_type = cdb[2] & 0xf;
- struct
- {
- struct prout_param_descriptor descr;
- struct transportid *trnptid_list_storage[MPATH_MX_TIDS];
- } paramp;
- struct transportid **trnptid_list = paramp.descr.trnptid_list;
+ g_autofree struct prout_param_descriptor *paramp = NULL;
char transportids[PR_HELPER_DATA_SIZE];
int r;
+ paramp = g_malloc0(sizeof(struct prout_param_descriptor)
+ + sizeof(struct transportid *) * MPATH_MX_TIDS);
+
if (sz < PR_OUT_FIXED_PARAM_SIZE) {
/* Illegal request, Parameter list length error. This isn't fatal;
* we have read the data, send an error without closing the socket.
@@ -459,10 +457,9 @@ static int multipath_pr_out(int fd, const uint8_t *cdb,
uint8_t *sense,
* used by libmpathpersist (which, of course, will immediately
* do the opposite).
*/
- memset(¶mp, 0, sizeof(paramp));
- memcpy(¶mp.descr.key, ¶m[0], 8);
- memcpy(¶mp.descr.sa_key, ¶m[8], 8);
- paramp.descr.sa_flags = param[20];
+ memcpy(¶mp->key, ¶m[0], 8);
+ memcpy(¶mp->sa_key, ¶m[8], 8);
+ paramp->sa_flags = param[20];
if (sz > PR_OUT_FIXED_PARAM_SIZE) {
size_t transportid_len;
int i, j;
@@ -525,13 +522,13 @@ static int multipath_pr_out(int fd, const uint8_t *cdb,
uint8_t *sense,
return CHECK_CONDITION;
}
- assert(paramp.descr.num_transportid < MPATH_MX_TIDS);
- trnptid_list[paramp.descr.num_transportid++] = id;
+ assert(paramp->num_transportid < MPATH_MX_TIDS);
+ paramp->trnptid_list[paramp->num_transportid++] = id;
}
}
r = mpath_persistent_reserve_out(fd, rq_servact, rq_scope, rq_type,
- ¶mp.descr, noisy, verbose);
+ paramp, noisy, verbose);
return mpath_reconstruct_sense(fd, r, sense);
}
#endif