On Tue, 4 Apr 2006 16:59:47 -0700 [email protected] wrote: > No one should be writing a PAGE_SIZE worth of data to a normal sysfs > file, so properly terminate the buffer. > > Thanks to Al Viro for pointing out my stupidity here. > > CVE-2006-1055 has been assigned for this. > > Signed-off-by: Greg Kroah-Hartman <[email protected]> > > --- > fs/sysfs/file.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > --- linux-2.6.16.1.orig/fs/sysfs/file.c > +++ linux-2.6.16.1/fs/sysfs/file.c > @@ -183,7 +183,7 @@ fill_write_buffer(struct sysfs_buffer * > return -ENOMEM; > > if (count >= PAGE_SIZE) > - count = PAGE_SIZE; > + count = PAGE_SIZE - 1; > error = copy_from_user(buffer->page,buf,count); > buffer->needs_read_fill = 1; > return error ? -EFAULT : count; This will break the "color_map" sysfs file for framebuffers - drivers/video/fbsysfs.c:store_cmap() expects to get exactly 4096 bytes for a colormap with 256 entries. In fact, the original patch which changed PAGE_SIZE - 1 to PAGE_SIZE: http://kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=9d9d27fb651a7c95a46f276bacb4329db47470a6 was done exactly for use with that "color_map" file. This patch also does not completely guarantee that the buffer will be null-terminated. A program may first call read() on the sysfs file, which will allocate buffer->page and invoke ->show to fill that page; then subsequent write() on the same file will reuse buffer->page. To get really bad results, you need to have ->store which assumes null-terminated buffer together with ->show which writes to the last byte of the page (which is probably rare, but show_cmap() does exactly that).
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