procfs: add 'path' to /proc/<pid>/fdinfo/

In order to identify the type of memory a process has pinned through its
open fds, add the file path to fdinfo output.  This allows identifying
memory types based on common prefixes: e.g.  "/memfd...", "/dmabuf...",
"/dev/ashmem...".

To be cautious, only expose the paths for anonymous inodes, and this also
avoids printing path names with strange characters.

Access to /proc/<pid>/fdinfo is governed by PTRACE_MODE_READ_FSCREDS the
same as /proc/<pid>/maps which also exposes the file path of mappings; so
the security permissions for accessing path is consistent with that of
/proc/<pid>/maps.

Link: https://lkml.kernel.org/r/20220623220613.3014268-3-kaleshsingh@google.com
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian König <christian.koenig@amd.com>
Cc: Christoph Anton Mitterer <mail@christoph.anton.mitterer.name>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Colin Cross <ccross@google.com>
Cc: David Laight <David.Laight@ACULAB.COM>
Cc: Ioannis Ilkos <ilkos@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Paul Gortmaker<paul.gortmaker@windriver.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Stephen Brennan <stephen.s.brennan@oracle.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: T.J. Mercier <tjmercier@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index 640fe47586e3e618b9bf50403acd5bd58a07f094..47e95dbc820d56bbf40561ec00a4a82bdb42bcd3 100644 (file)
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -1912,6 +1912,9 @@ All locks associated with a file descriptor are shown in its fdinfo too::
 
     lock:       1: FLOCK  ADVISORY  WRITE 359 00:13:11691 0 EOF
 
+Files with anonymous inodes have an additional 'path' field which represents
+the anonymous file path.
+
 The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
 pair provide additional information particular to the objects they represent.
 
@@ -1925,6 +1928,7 @@ Eventfd files
        mnt_id: 9
        ino:    63107
        size:   0
+       path:   anon_inode:[eventfd]
        eventfd-count:  5a
 
 where 'eventfd-count' is hex value of a counter.
@@ -1939,6 +1943,7 @@ Signalfd files
        mnt_id: 9
        ino:    63107
        size:   0
+       path:   anon_inode:[signalfd]
        sigmask:        0000000000000200
 
 where 'sigmask' is hex value of the signal mask associated
@@ -1954,6 +1959,7 @@ Epoll files
        mnt_id: 9
        ino:    63107
        size:   0
+       path:   anon_inode:[eventpoll]
        tfd:        5 events:       1d data: ffffffffffffffff pos:0 ino:61af sdev:7
 
 where 'tfd' is a target file descriptor number in decimal form,
@@ -1973,6 +1979,7 @@ For inotify files the format is the following::
        mnt_id: 9
        ino:    63107
        size:   0
+       path:   anon_inode:inotify
        inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
 
 where 'wd' is a watch descriptor in decimal form, i.e. a target file
@@ -1997,6 +2004,7 @@ For fanotify files the format is::
        mnt_id: 9
        ino:    63107
        size:   0
+       path:   anon_inode:[fanotify]
        fanotify flags:10 event-flags:0
        fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
        fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
@@ -2023,6 +2031,7 @@ Timerfd files
        mnt_id: 9
        ino:    63107
        size:   0
+       path:   anon_inode:[timerfd]
        clockid: 0
        ticks: 0
        settime flags: 01
@@ -2047,6 +2056,7 @@ DMA Buffer files
        mnt_id: 9
        ino:    63107
        size:   32768
+       path:   /dmabuf:
        count:  2
        exp_name:  system-heap
 

diff --git a/fs/libfs.c b/fs/libfs.c
index 31b0ddf01c31daca6a946c48c78b5d821034e0c0..6911749b4da79dea0252bb28892b43c7b6cb8d76 100644 (file)
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -1217,6 +1217,15 @@ void kfree_link(void *p)
 }
 EXPORT_SYMBOL(kfree_link);
 
+static const struct address_space_operations anon_aops = {
+       .dirty_folio    = noop_dirty_folio,
+};
+
+bool is_anon_inode(struct inode *inode)
+{
+       return inode->i_mapping->a_ops == &anon_aops;
+}
+
 struct inode *alloc_anon_inode(struct super_block *s)
 {
        static const struct address_space_operations anon_aops = {

diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 464bc3f557596b7fd73e8410214cc2bcd0e613dc..5bac79a2fa515baf92ab7b078d17869d7f29d696 100644 (file)
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -23,6 +23,7 @@ static int seq_show(struct seq_file *m, void *v)
        struct files_struct *files = NULL;
        int f_flags = 0, ret = -ENOENT;
        struct file *file = NULL;
+       struct inode *inode = NULL;
        struct task_struct *task;
 
        task = get_proc_task(m->private);
@@ -54,11 +55,19 @@ static int seq_show(struct seq_file *m, void *v)
        if (ret)
                return ret;
 
+       inode = file_inode(file);
+
        seq_printf(m, "pos:\t%lli\n", (long long)file->f_pos);
        seq_printf(m, "flags:\t0%o\n", f_flags);
        seq_printf(m, "mnt_id:\t%i\n", real_mount(file->f_path.mnt)->mnt_id);
-       seq_printf(m, "ino:\t%lu\n", file_inode(file)->i_ino);
-       seq_printf(m, "size:\t%lli\n", (long long)file_inode(file)->i_size);
+       seq_printf(m, "ino:\t%lu\n", inode->i_ino);
+       seq_printf(m, "size:\t%lli\n", (long long)inode->i_size);
+
+       if (is_anon_inode(inode)) {
+               seq_puts(m, "path:\t");
+               seq_file_path(m, file, "\n");
+               seq_putc(m, '\n');
+       }
 
        /* show_fd_locks() never deferences files so a stale value is safe */
        show_fd_locks(m, file, files);

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 9eced4cc286ee18ad996c337be92ba6fc9f57111..a98b03857440653ee7a5532436ed4a6525d319d4 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3249,6 +3249,7 @@ extern void page_put_link(void *);
 extern int page_symlink(struct inode *inode, const char *symname, int len);
 extern const struct inode_operations page_symlink_inode_operations;
 extern void kfree_link(void *);
+extern bool is_anon_inode(struct inode *inode);
 void generic_fillattr(struct user_namespace *, struct inode *, struct kstat *);
 void generic_fill_statx_attr(struct inode *inode, struct kstat *stat);
 extern int vfs_getattr_nosec(const struct path *, struct kstat *, u32, unsigned int);