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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, 2 Mar 2020 16:38:24 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 |
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;
> | ^~~~~~
Ouch. Very nice new warning.
Cc: address@hidden
Queued, thanks.
> 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 is to replace `paramp` with an anonymous struct that adds
> additional space for the data, called `trnptid_list_storage`.
> That space provides MATH_MX_TIDS entries, and is not accessed directly
> but through a pointer to `descr.trnptid_list`, in the unlikely case a
> future compiler inserts some padding between the two structs.
>
> Signed-off-by: Christophe de Dinechin <address@hidden>
> ---
> scsi/qemu-pr-helper.c | 18 ++++++++++++------
> 1 file changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/scsi/qemu-pr-helper.c b/scsi/qemu-pr-helper.c
> index 0659ceef09..01013221b3 100644
> --- a/scsi/qemu-pr-helper.c
> +++ b/scsi/qemu-pr-helper.c
> @@ -421,7 +421,12 @@ 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 prout_param_descriptor paramp;
> + struct
> + {
> + struct prout_param_descriptor descr;
> + struct transportid *trnptid_list_storage[MPATH_MX_TIDS];
> + } paramp;
> + struct transportid **trnptid_list = paramp.descr.trnptid_list;
> char transportids[PR_HELPER_DATA_SIZE];
> int r;
>
> @@ -455,9 +460,9 @@ static int multipath_pr_out(int fd, const uint8_t *cdb,
> uint8_t *sense,
> * do the opposite).
> */
> memset(¶mp, 0, sizeof(paramp));
> - memcpy(¶mp.key, ¶m[0], 8);
> - memcpy(¶mp.sa_key, ¶m[8], 8);
> - paramp.sa_flags = param[20];
> + memcpy(¶mp.descr.key, ¶m[0], 8);
> + memcpy(¶mp.descr.sa_key, ¶m[8], 8);
> + paramp.descr.sa_flags = param[20];
> if (sz > PR_OUT_FIXED_PARAM_SIZE) {
> size_t transportid_len;
> int i, j;
> @@ -520,12 +525,13 @@ static int multipath_pr_out(int fd, const uint8_t *cdb,
> uint8_t *sense,
> return CHECK_CONDITION;
> }
>
> - paramp.trnptid_list[paramp.num_transportid++] = id;
> + assert(paramp.descr.num_transportid < MPATH_MX_TIDS);
> + trnptid_list[paramp.descr.num_transportid++] = id;
> }
> }
>
> r = mpath_persistent_reserve_out(fd, rq_servact, rq_scope, rq_type,
> - ¶mp, noisy, verbose);
> + ¶mp.descr, noisy, verbose);
> return mpath_reconstruct_sense(fd, r, sense);
> }
> #endif
>
- Re: [PATCH] scsi/qemu-pr-helper: Fix out-of-bounds access to trnptid_list[],
Paolo Bonzini <=