* [PATCH driver-core-linus] sysfs: make sure read buffer is zeroed [not found] <20140519172334.GK20439@audi.shelbyville.oz> @ 2014-05-19 19:52 ` Tejun Heo 2014-05-19 22:25 ` Greg Kroah-Hartman 0 siblings, 1 reply; 5+ messages in thread From: Tejun Heo @ 2014-05-19 19:52 UTC (permalink / raw) To: Greg Kroah-Hartman, linux-kernel; +Cc: Kay Sievers, Ron, Ben Hutchings 13c589d5b0ac ("sysfs: use seq_file when reading regular files") switched sysfs from custom read implementation to seq_file to enable later transition to kernfs. After the change, the buffer passed to ->show() is acquired through seq_get_buf(); unfortunately, this introduces a subtle behavior change. Before the commit, the buffer passed to ->show() was always zero as it was allocated using get_zeroed_page(). Because seq_file doesn't clear buffers on allocation and neither does seq_get_buf(), after the commit, depending on the behavior of ->show(), we may end up exposing uninitialized data to userland thus possibly altering userland visible behavior and leaking information. Fix it by explicitly clearing the buffer. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Ron <ron@debian.org> Fixes: 13c589d5b0ac ("sysfs: use seq_file when reading regular files") --- fs/sysfs/file.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c index 28cc1acd..e9ef59b 100644 --- a/fs/sysfs/file.c +++ b/fs/sysfs/file.c @@ -47,12 +47,13 @@ static int sysfs_kf_seq_show(struct seq_file *sf, void *v) ssize_t count; char *buf; - /* acquire buffer and ensure that it's >= PAGE_SIZE */ + /* acquire buffer and ensure that it's >= PAGE_SIZE and clear */ count = seq_get_buf(sf, &buf); if (count < PAGE_SIZE) { seq_commit(sf, -1); return 0; } + memset(buf, 0, PAGE_SIZE); /* * Invoke show(). Control may reach here via seq file lseek even ^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH driver-core-linus] sysfs: make sure read buffer is zeroed 2014-05-19 19:52 ` [PATCH driver-core-linus] sysfs: make sure read buffer is zeroed Tejun Heo @ 2014-05-19 22:25 ` Greg Kroah-Hartman 2014-05-19 22:32 ` Joe Perches 0 siblings, 1 reply; 5+ messages in thread From: Greg Kroah-Hartman @ 2014-05-19 22:25 UTC (permalink / raw) To: Tejun Heo; +Cc: linux-kernel, Kay Sievers, Ron, Ben Hutchings On Mon, May 19, 2014 at 03:52:10PM -0400, Tejun Heo wrote: > 13c589d5b0ac ("sysfs: use seq_file when reading regular files") > switched sysfs from custom read implementation to seq_file to enable > later transition to kernfs. After the change, the buffer passed to > ->show() is acquired through seq_get_buf(); unfortunately, this > introduces a subtle behavior change. Before the commit, the buffer > passed to ->show() was always zero as it was allocated using > get_zeroed_page(). Because seq_file doesn't clear buffers on > allocation and neither does seq_get_buf(), after the commit, depending > on the behavior of ->show(), we may end up exposing uninitialized data > to userland thus possibly altering userland visible behavior and > leaking information. > > Fix it by explicitly clearing the buffer. > > Signed-off-by: Tejun Heo <tj@kernel.org> > Reported-by: Ron <ron@debian.org> > Fixes: 13c589d5b0ac ("sysfs: use seq_file when reading regular files") > --- > fs/sysfs/file.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c > index 28cc1acd..e9ef59b 100644 > --- a/fs/sysfs/file.c > +++ b/fs/sysfs/file.c > @@ -47,12 +47,13 @@ static int sysfs_kf_seq_show(struct seq_file *sf, void *v) > ssize_t count; > char *buf; > > - /* acquire buffer and ensure that it's >= PAGE_SIZE */ > + /* acquire buffer and ensure that it's >= PAGE_SIZE and clear */ > count = seq_get_buf(sf, &buf); > if (count < PAGE_SIZE) { > seq_commit(sf, -1); > return 0; > } > + memset(buf, 0, PAGE_SIZE); > > /* > * Invoke show(). Control may reach here via seq file lseek even Thanks, I'll go queue this up. greg k-h ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH driver-core-linus] sysfs: make sure read buffer is zeroed 2014-05-19 22:25 ` Greg Kroah-Hartman @ 2014-05-19 22:32 ` Joe Perches 2014-05-20 0:49 ` Tejun Heo 0 siblings, 1 reply; 5+ messages in thread From: Joe Perches @ 2014-05-19 22:32 UTC (permalink / raw) To: Greg Kroah-Hartman Cc: Tejun Heo, linux-kernel, Kay Sievers, Ron, Ben Hutchings On Mon, 2014-05-19 at 15:25 -0700, Greg Kroah-Hartman wrote: > On Mon, May 19, 2014 at 03:52:10PM -0400, Tejun Heo wrote: > > 13c589d5b0ac ("sysfs: use seq_file when reading regular files") > > switched sysfs from custom read implementation to seq_file to enable > > later transition to kernfs. After the change, the buffer passed to > > ->show() is acquired through seq_get_buf(); unfortunately, this > > introduces a subtle behavior change. Before the commit, the buffer > > passed to ->show() was always zero as it was allocated using > > get_zeroed_page(). Because seq_file doesn't clear buffers on > > allocation and neither does seq_get_buf(), after the commit, depending > > on the behavior of ->show(), we may end up exposing uninitialized data > > to userland thus possibly altering userland visible behavior and > > leaking information. > > > > Fix it by explicitly clearing the buffer. [] > > diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c [] > > @@ -47,12 +47,13 @@ static int sysfs_kf_seq_show(struct seq_file *sf, void *v) > > ssize_t count; > > char *buf; > > > > - /* acquire buffer and ensure that it's >= PAGE_SIZE */ > > + /* acquire buffer and ensure that it's >= PAGE_SIZE and clear */ > > count = seq_get_buf(sf, &buf); > > if (count < PAGE_SIZE) { > > seq_commit(sf, -1); > > return 0; > > } > > + memset(buf, 0, PAGE_SIZE); memset(buf, 0, count)? > Thanks, I'll go queue this up. ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH driver-core-linus] sysfs: make sure read buffer is zeroed 2014-05-19 22:32 ` Joe Perches @ 2014-05-20 0:49 ` Tejun Heo 2014-05-20 1:25 ` Joe Perches 0 siblings, 1 reply; 5+ messages in thread From: Tejun Heo @ 2014-05-20 0:49 UTC (permalink / raw) To: Joe Perches Cc: Greg Kroah-Hartman, linux-kernel, Kay Sievers, Ron, Ben Hutchings On Mon, May 19, 2014 at 03:32:22PM -0700, Joe Perches wrote: > > > + memset(buf, 0, PAGE_SIZE); > > memset(buf, 0, count)? It's always PAGE_SIZE. Outputs longer than that are truncated. Thanks. -- tejun ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH driver-core-linus] sysfs: make sure read buffer is zeroed 2014-05-20 0:49 ` Tejun Heo @ 2014-05-20 1:25 ` Joe Perches 0 siblings, 0 replies; 5+ messages in thread From: Joe Perches @ 2014-05-20 1:25 UTC (permalink / raw) To: Tejun Heo Cc: Greg Kroah-Hartman, linux-kernel, Kay Sievers, Ron, Ben Hutchings On Mon, 2014-05-19 at 20:49 -0400, Tejun Heo wrote: > On Mon, May 19, 2014 at 03:32:22PM -0700, Joe Perches wrote: > > > > + memset(buf, 0, PAGE_SIZE); > > > > memset(buf, 0, count)? > > It's always PAGE_SIZE. Outputs longer than that are truncated. Yeah, I know, but the code and comment above it don't match. /* acquire buffer and ensure that it's >= PAGE_SIZE and clear */ ^ permalink raw reply [flat|nested] 5+ messages in thread
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[not found] <20140519172334.GK20439@audi.shelbyville.oz>
2014-05-19 19:52 ` [PATCH driver-core-linus] sysfs: make sure read buffer is zeroed Tejun Heo
2014-05-19 22:25 ` Greg Kroah-Hartman
2014-05-19 22:32 ` Joe Perches
2014-05-20 0:49 ` Tejun Heo
2014-05-20 1:25 ` Joe Perches
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