Messages in this thread | | | Date | Fri, 22 May 2015 02:04:31 +0300 | From | Vladimir Zapolskiy <> | Subject | Re: [PATCH] fs: sysfs: don't pass count == 0 to bin file readers |
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Hello Tejun,
On 22.05.2015 01:14, Tejun Heo wrote: > Hello, > > On Fri, May 22, 2015 at 12:21:16AM +0300, Vladimir Zapolskiy wrote: >> If count == 0 bytes are requested by a reader, sysfs_kf_bin_read() >> deliberately returns 0 without passing a potentially harmful value to >> some externally defined underlying battr->read() function. >> >> However in case of (pos == size && count) the next clause always sets >> count to 0 and this value is handed over to battr->read(). >> >> The change intends to make obsolete (and remove later) a redundant >> sanity check in battr->read(), if it is present, or add more >> protection to struct bin_attribute users, who does not care about >> input arguments. >> >> Signed-off-by: Vladimir Zapolskiy <vz@mleia.com> >> --- >> fs/sysfs/file.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c >> index 7c2867b..6c95628 100644 >> --- a/fs/sysfs/file.c >> +++ b/fs/sysfs/file.c >> @@ -90,7 +90,7 @@ static ssize_t sysfs_kf_bin_read(struct kernfs_open_file *of, char *buf, >> return 0; >> >> if (size) { >> - if (pos > size) >> + if (pos >= size) >> return 0; >> if (pos + count > size) >> count = size - pos; > > Hmmm... maybe just move that test upwards? > > if (!count || pos >= size) > return 0; > > count = min(count, size - pos); >
If the code block stays within if (size && count) { ... }, then !count check is redundant (you may notice that !count check is already present above but not shown in diff's 3 lines context), and I agree that
if (pos >= size) return 0;
if (pos + count > size) count = size - pos;
and
if (pos >= size) return 0;
count = min(count, size - pos);
are equal.
But "!size" is a special case,
if (!count || pos >= size) return 0;
seems to be incorrect in case of !size ===> (pos >= size) == true.
To the sent change I may add a replacement of "if (pos + count > size) ..." with min_t (ssize_t, count, size - pos), if you wish.
-- With best wishes, Vladimir
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