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Date: Sat, 19 May 2018 04:43:38 +0100 From: Al Viro <viro@...IV.linux.org.uk> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: gor@...ux.ibm.com, Andrew Morton <akpm@...ux-foundation.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Heiko Carstens <heiko.carstens@...ibm.com> Subject: Re: [PATCH] procfs: fix mmap() for /proc/vmcore On Fri, May 18, 2018 at 08:33:37PM -0700, Linus Torvalds wrote: > On Fri, May 18, 2018 at 8:20 PM Linus Torvalds < > torvalds@...ux-foundation.org> wrote: > > > I'd *much* rather just set FMODE_UNSIGNED_OFFSET for /proc/vmcore _only_, > > rather than open up all proc files to issues with 4G+ offsets. > > Hmm. I was going to point to the s_maxbytes check in rw_verify_area() and > ask you how that ever worked for that file, but it's not there, the > s_maxbyte checks are only in lseek and in do_splice(). > > So apparently we protect against llseek + read/write, but we don't protect > against pread64/pwrite64 having offset overflows.. > > That's crazy. That makes all the s_maxbytes protection much less effective > than it should be. Filesystems that don't get the 64-bit case right will > screw up pread64 and friends. > > Al, I'm missing something. Did we always have this gaping hole where we > didn't actually check s_maxbytes against read/write, only > generic_file_llseek? Apparently. Not quite. The things like if (unlikely(*ppos >= inode->i_sb->s_maxbytes)) return 0; iov_iter_truncate(iter, inode->i_sb->s_maxbytes); protect most of the regular files (see mm/filemap.c). And for devices (which is where the majority of crap ->read()/->write() is) it's obviously not applicable - ->s_maxbytes of *what*?
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