From: Linus Torvalds Date: Tue, 21 Jan 2025 17:27:22 +0000 (-0800) Subject: cachestat: fix page cache statistics permission checking X-Git-Tag: nvme-6.14-2025-03-05~47 X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=5f537664e705b0bf8b7e329861f20128534f6a83;p=nvme.git cachestat: fix page cache statistics permission checking When the 'cachestat()' system call was added in commit cf264e1329fb ("cachestat: implement cachestat syscall"), it was meant to be a much more convenient (and performant) version of mincore() that didn't need mapping things into the user virtual address space in order to work. But it ended up missing the "check for writability or ownership" fix for mincore(), done in commit 134fca9063ad ("mm/mincore.c: make mincore() more conservative"). This just adds equivalent logic to 'cachestat()', modified for the file context (rather than vma). Reported-by: Sudheendra Raghav Neela Fixes: cf264e1329fb ("cachestat: implement cachestat syscall") Tested-by: Johannes Weiner Acked-by: Johannes Weiner Acked-by: Nhat Pham Signed-off-by: Linus Torvalds --- diff --git a/mm/filemap.c b/mm/filemap.c index 4f476411a9a2..440922a7d8f1 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -4375,6 +4375,20 @@ resched: rcu_read_unlock(); } +/* + * See mincore: reveal pagecache information only for files + * that the calling process has write access to, or could (if + * tried) open for writing. + */ +static inline bool can_do_cachestat(struct file *f) +{ + if (f->f_mode & FMODE_WRITE) + return true; + if (inode_owner_or_capable(file_mnt_idmap(f), file_inode(f))) + return true; + return file_permission(f, MAY_WRITE) == 0; +} + /* * The cachestat(2) system call. * @@ -4430,6 +4444,9 @@ SYSCALL_DEFINE4(cachestat, unsigned int, fd, if (is_file_hugepages(fd_file(f))) return -EOPNOTSUPP; + if (!can_do_cachestat(fd_file(f))) + return -EPERM; + if (flags != 0) return -EINVAL;