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splice: fix racy pipe->buffers uses
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Dave Jones reported a kernel BUG at mm/slub.c:3474! triggered
by splice_shrink_spd() called from vmsplice_to_pipe()

commit 35f3d14 (pipe: add support for shrinking and growing pipes)
added capability to adjust pipe->buffers.

Problem is some paths don't hold pipe mutex and assume pipe->buffers
doesn't change for their duration.

Fix this by adding nr_pages_max field in struct splice_pipe_desc, and
use it in place of pipe->buffers where appropriate.

splice_shrink_spd() loses its struct pipe_inode_info argument.

Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Tom Herbert <therbert@google.com>
Cc: stable <stable@vger.kernel.org> # 2.6.35
Tested-by: Dave Jones <davej@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Eric Dumazet authored and axboe committed Jun 13, 2012
1 parent 27e1f9d commit 047fe36
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Showing 6 changed files with 34 additions and 24 deletions.
35 changes: 20 additions & 15 deletions fs/splice.c
View file
Expand Up @@ -273,13 +273,16 @@ void spd_release_page(struct splice_pipe_desc *spd, unsigned int i)
* Check if we need to grow the arrays holding pages and partial page
* descriptions.
*/
int splice_grow_spd(struct pipe_inode_info *pipe, struct splice_pipe_desc *spd)
int splice_grow_spd(const struct pipe_inode_info *pipe, struct splice_pipe_desc *spd)
{
if (pipe->buffers <= PIPE_DEF_BUFFERS)
unsigned int buffers = ACCESS_ONCE(pipe->buffers);

spd->nr_pages_max = buffers;
if (buffers <= PIPE_DEF_BUFFERS)
return 0;

spd->pages = kmalloc(pipe->buffers * sizeof(struct page *), GFP_KERNEL);
spd->partial = kmalloc(pipe->buffers * sizeof(struct partial_page), GFP_KERNEL);
spd->pages = kmalloc(buffers * sizeof(struct page *), GFP_KERNEL);
spd->partial = kmalloc(buffers * sizeof(struct partial_page), GFP_KERNEL);

if (spd->pages && spd->partial)
return 0;
Expand All @@ -289,10 +292,9 @@ int splice_grow_spd(struct pipe_inode_info *pipe, struct splice_pipe_desc *spd)
return -ENOMEM;
}

void splice_shrink_spd(struct pipe_inode_info *pipe,
struct splice_pipe_desc *spd)
void splice_shrink_spd(struct splice_pipe_desc *spd)
{
if (pipe->buffers <= PIPE_DEF_BUFFERS)
if (spd->nr_pages_max <= PIPE_DEF_BUFFERS)
return;

kfree(spd->pages);
Expand All @@ -315,6 +317,7 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
struct splice_pipe_desc spd = {
.pages = pages,
.partial = partial,
.nr_pages_max = PIPE_DEF_BUFFERS,
.flags = flags,
.ops = &page_cache_pipe_buf_ops,
.spd_release = spd_release_page,
Expand All @@ -326,7 +329,7 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
index = *ppos >> PAGE_CACHE_SHIFT;
loff = *ppos & ~PAGE_CACHE_MASK;
req_pages = (len + loff + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
nr_pages = min(req_pages, pipe->buffers);
nr_pages = min(req_pages, spd.nr_pages_max);

/*
* Lookup the (hopefully) full range of pages we need.
Expand Down Expand Up @@ -497,7 +500,7 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
if (spd.nr_pages)
error = splice_to_pipe(pipe, &spd);

splice_shrink_spd(pipe, &spd);
splice_shrink_spd(&spd);
return error;
}

Expand Down Expand Up @@ -598,6 +601,7 @@ ssize_t default_file_splice_read(struct file *in, loff_t *ppos,
struct splice_pipe_desc spd = {
.pages = pages,
.partial = partial,
.nr_pages_max = PIPE_DEF_BUFFERS,
.flags = flags,
.ops = &default_pipe_buf_ops,
.spd_release = spd_release_page,
Expand All @@ -608,16 +612,16 @@ ssize_t default_file_splice_read(struct file *in, loff_t *ppos,

res = -ENOMEM;
vec = __vec;
if (pipe->buffers > PIPE_DEF_BUFFERS) {
vec = kmalloc(pipe->buffers * sizeof(struct iovec), GFP_KERNEL);
if (spd.nr_pages_max > PIPE_DEF_BUFFERS) {
vec = kmalloc(spd.nr_pages_max * sizeof(struct iovec), GFP_KERNEL);
if (!vec)
goto shrink_ret;
}

offset = *ppos & ~PAGE_CACHE_MASK;
nr_pages = (len + offset + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;

for (i = 0; i < nr_pages && i < pipe->buffers && len; i++) {
for (i = 0; i < nr_pages && i < spd.nr_pages_max && len; i++) {
struct page *page;

page = alloc_page(GFP_USER);
Expand Down Expand Up @@ -665,7 +669,7 @@ ssize_t default_file_splice_read(struct file *in, loff_t *ppos,
shrink_ret:
if (vec != __vec)
kfree(vec);
splice_shrink_spd(pipe, &spd);
splice_shrink_spd(&spd);
return res;

err:
Expand Down Expand Up @@ -1614,6 +1618,7 @@ static long vmsplice_to_pipe(struct file *file, const struct iovec __user *iov,
struct splice_pipe_desc spd = {
.pages = pages,
.partial = partial,
.nr_pages_max = PIPE_DEF_BUFFERS,
.flags = flags,
.ops = &user_page_pipe_buf_ops,
.spd_release = spd_release_page,
Expand All @@ -1629,13 +1634,13 @@ static long vmsplice_to_pipe(struct file *file, const struct iovec __user *iov,

spd.nr_pages = get_iovec_page_array(iov, nr_segs, spd.pages,
spd.partial, false,
pipe->buffers);
spd.nr_pages_max);
if (spd.nr_pages <= 0)
ret = spd.nr_pages;
else
ret = splice_to_pipe(pipe, &spd);

splice_shrink_spd(pipe, &spd);
splice_shrink_spd(&spd);
return ret;
}

Expand Down
8 changes: 4 additions & 4 deletions include/linux/splice.h
View file
Expand Up @@ -51,7 +51,8 @@ struct partial_page {
struct splice_pipe_desc {
struct page **pages; /* page map */
struct partial_page *partial; /* pages[] may not be contig */
int nr_pages; /* number of pages in map */
int nr_pages; /* number of populated pages in map */
unsigned int nr_pages_max; /* pages[] & partial[] arrays size */
unsigned int flags; /* splice flags */
const struct pipe_buf_operations *ops;/* ops associated with output pipe */
void (*spd_release)(struct splice_pipe_desc *, unsigned int);
Expand Down Expand Up @@ -85,9 +86,8 @@ extern ssize_t splice_direct_to_actor(struct file *, struct splice_desc *,
/*
* for dynamic pipe sizing
*/
extern int splice_grow_spd(struct pipe_inode_info *, struct splice_pipe_desc *);
extern void splice_shrink_spd(struct pipe_inode_info *,
struct splice_pipe_desc *);
extern int splice_grow_spd(const struct pipe_inode_info *, struct splice_pipe_desc *);
extern void splice_shrink_spd(struct splice_pipe_desc *);
extern void spd_release_page(struct splice_pipe_desc *, unsigned int);

extern const struct pipe_buf_operations page_cache_pipe_buf_ops;
Expand Down
5 changes: 3 additions & 2 deletions kernel/relay.c
View file
Expand Up @@ -1235,6 +1235,7 @@ static ssize_t subbuf_splice_actor(struct file *in,
struct splice_pipe_desc spd = {
.pages = pages,
.nr_pages = 0,
.nr_pages_max = PIPE_DEF_BUFFERS,
.partial = partial,
.flags = flags,
.ops = &relay_pipe_buf_ops,
Expand Down Expand Up @@ -1302,8 +1303,8 @@ static ssize_t subbuf_splice_actor(struct file *in,
ret += padding;

out:
splice_shrink_spd(pipe, &spd);
return ret;
splice_shrink_spd(&spd);
return ret;
}

static ssize_t relay_file_splice_read(struct file *in,
Expand Down
6 changes: 4 additions & 2 deletions kernel/trace/trace.c
View file
Expand Up @@ -3609,6 +3609,7 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
.pages = pages_def,
.partial = partial_def,
.nr_pages = 0, /* This gets updated below. */
.nr_pages_max = PIPE_DEF_BUFFERS,
.flags = flags,
.ops = &tracing_pipe_buf_ops,
.spd_release = tracing_spd_release_pipe,
Expand Down Expand Up @@ -3680,7 +3681,7 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,

ret = splice_to_pipe(pipe, &spd);
out:
splice_shrink_spd(pipe, &spd);
splice_shrink_spd(&spd);
return ret;

out_err:
Expand Down Expand Up @@ -4231,6 +4232,7 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
struct splice_pipe_desc spd = {
.pages = pages_def,
.partial = partial_def,
.nr_pages_max = PIPE_DEF_BUFFERS,
.flags = flags,
.ops = &buffer_pipe_buf_ops,
.spd_release = buffer_spd_release,
Expand Down Expand Up @@ -4318,7 +4320,7 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
}

ret = splice_to_pipe(pipe, &spd);
splice_shrink_spd(pipe, &spd);
splice_shrink_spd(&spd);
out:
return ret;
}
Expand Down
3 changes: 2 additions & 1 deletion mm/shmem.c
View file
Expand Up @@ -1577,6 +1577,7 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
struct splice_pipe_desc spd = {
.pages = pages,
.partial = partial,
.nr_pages_max = PIPE_DEF_BUFFERS,
.flags = flags,
.ops = &page_cache_pipe_buf_ops,
.spd_release = spd_release_page,
Expand Down Expand Up @@ -1665,7 +1666,7 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
if (spd.nr_pages)
error = splice_to_pipe(pipe, &spd);

splice_shrink_spd(pipe, &spd);
splice_shrink_spd(&spd);

if (error > 0) {
*ppos += error;
Expand Down
1 change: 1 addition & 0 deletions net/core/skbuff.c
View file
Expand Up @@ -1755,6 +1755,7 @@ int skb_splice_bits(struct sk_buff *skb, unsigned int offset,
struct splice_pipe_desc spd = {
.pages = pages,
.partial = partial,
.nr_pages_max = MAX_SKB_FRAGS,
.flags = flags,
.ops = &sock_pipe_buf_ops,
.spd_release = sock_spd_release,
Expand Down

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