Processes can pin shared memory by keeping a handle to it through a file descriptor; for instance dmabufs, memfd, and ashmem (in Android).
In the case of a memory leak, to identify the process pinning the memory, userspace needs to: - Iterate the /proc/<pid>/fd/* for each process - Do a readlink on each entry to identify the type of memory from the file path. - stat() each entry to get the size of the memory.
The file permissions on /proc/<pid>/fd/* only allows for the owner or root to perform the operations above; and so is not suitable for capturing the system-wide state in a production environment.
This issue was addressed for dmabufs by making /proc/*/fdinfo/* accessible to a process with PTRACE_MODE_READ_FSCREDS credentials[1] To allow the same kind of tracking for other types of shared memory, add the following fields to /proc/<pid>/fdinfo/<fd>:
path - This allows identifying the type of memory based on common prefixes: e.g. "/memfd...", "/dmabuf...", "/dev/ashmem..."
This was not an issued when dmabuf tracking was introduced because the exp_name field of dmabuf fdinfo could be used to distinguish dmabuf fds from other types.
size - To track the amount of memory that is being pinned.
dmabufs expose size as an additional field in fdinfo. Remove this and make it a common field for all fds.
Access to /proc/<pid>/fdinfo is governed by PTRACE_MODE_READ_FSCREDS -- the same as for /proc/<pid>/maps which also exposes the path and size for mapped memory regions.
This allows for a system process with PTRACE_MODE_READ_FSCREDS to account the pinned per-process memory via fdinfo.
-----
There was some concern about exposing the file path in the RFC[2], to that effect the change was split into separte patches. Also retrieving the file path from fdinfo is guarded by the same capability (PTRACE_MODE_READ) as /proc/<pid>/maps which also exposes file path, so this may not be an issue.
[1] https://lore.kernel.org/r/20210308170651.919148-1-kaleshsingh@google.com/ [2] https://lore.kernel.org/r/20220519214021.3572840-1-kaleshsingh@google.com/
Kalesh Singh (2): procfs: Add 'size' to /proc/<pid>/fdinfo/ procfs: Add 'path' to /proc/<pid>/fdinfo/
Documentation/filesystems/proc.rst | 22 ++++++++++++++++++++-- drivers/dma-buf/dma-buf.c | 1 - fs/proc/fd.c | 13 +++++++++---- 3 files changed, 29 insertions(+), 7 deletions(-)
base-commit: 8ab2afa23bd197df47819a87f0265c0ac95c5b6a
To be able to account the amount of memory a process is keeping pinned by open file descriptors add a 'size' field to fdinfo output.
dmabufs fds already expose a 'size' field for this reason, remove this and make it a common field for all fds. This allows tracking of other types of memory (e.g. memfd and ashmem in Android).
Signed-off-by: Kalesh Singh kaleshsingh@google.com ---
Changes from rfc: - Split adding 'size' and 'path' into a separate patches, per Christian - Split fdinfo seq_printf into separate lines, per Christian - Fix indentation (use tabs) in documentaion, per Randy
Documentation/filesystems/proc.rst | 12 ++++++++++-- drivers/dma-buf/dma-buf.c | 1 - fs/proc/fd.c | 9 +++++---- 3 files changed, 15 insertions(+), 7 deletions(-)
diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst index 1bc91fb8c321..779c05528e87 100644 --- a/Documentation/filesystems/proc.rst +++ b/Documentation/filesystems/proc.rst @@ -1886,13 +1886,14 @@ if precise results are needed. 3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file --------------------------------------------------------------- This file provides information associated with an opened file. The regular -files have at least four fields -- 'pos', 'flags', 'mnt_id' and 'ino'. +files have at least five fields -- 'pos', 'flags', 'mnt_id', 'ino', and 'size'. + The 'pos' represents the current offset of the opened file in decimal form [see lseek(2) for details], 'flags' denotes the octal O_xxx mask the file has been created with [see open(2) for details] and 'mnt_id' represents mount ID of the file system containing the opened file [see 3.5 /proc/<pid>/mountinfo for details]. 'ino' represents the inode number of -the file. +the file, and 'size' represents the size of the file in bytes.
A typical output is::
@@ -1900,6 +1901,7 @@ A typical output is:: flags: 0100002 mnt_id: 19 ino: 63107 + size: 0
All locks associated with a file descriptor are shown in its fdinfo too::
@@ -1917,6 +1919,7 @@ Eventfd files flags: 04002 mnt_id: 9 ino: 63107 + size: 0 eventfd-count: 5a
where 'eventfd-count' is hex value of a counter. @@ -1930,6 +1933,7 @@ Signalfd files flags: 04002 mnt_id: 9 ino: 63107 + size: 0 sigmask: 0000000000000200
where 'sigmask' is hex value of the signal mask associated @@ -1944,6 +1948,7 @@ Epoll files flags: 02 mnt_id: 9 ino: 63107 + size: 0 tfd: 5 events: 1d data: ffffffffffffffff pos:0 ino:61af sdev:7
where 'tfd' is a target file descriptor number in decimal form, @@ -1962,6 +1967,7 @@ For inotify files the format is the following:: flags: 02000000 mnt_id: 9 ino: 63107 + size: 0 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 @@ -1985,6 +1991,7 @@ For fanotify files the format is:: flags: 02 mnt_id: 9 ino: 63107 + size: 0 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 @@ -2010,6 +2017,7 @@ Timerfd files flags: 02 mnt_id: 9 ino: 63107 + size: 0 clockid: 0 ticks: 0 settime flags: 01 diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 32f55640890c..5f2ae38c960f 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -378,7 +378,6 @@ static void dma_buf_show_fdinfo(struct seq_file *m, struct file *file) { struct dma_buf *dmabuf = file->private_data;
- seq_printf(m, "size:\t%zu\n", dmabuf->size); /* Don't count the temporary reference taken inside procfs seq_show */ seq_printf(m, "count:\t%ld\n", file_count(dmabuf->file) - 1); seq_printf(m, "exp_name:\t%s\n", dmabuf->exp_name); diff --git a/fs/proc/fd.c b/fs/proc/fd.c index 913bef0d2a36..464bc3f55759 100644 --- a/fs/proc/fd.c +++ b/fs/proc/fd.c @@ -54,10 +54,11 @@ static int seq_show(struct seq_file *m, void *v) if (ret) return ret;
- seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\nino:\t%lu\n", - (long long)file->f_pos, f_flags, - real_mount(file->f_path.mnt)->mnt_id, - file_inode(file)->i_ino); + 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);
/* show_fd_locks() never deferences files so a stale value is safe */ show_fd_locks(m, file, files);
Am 31.05.22 um 23:25 schrieb Kalesh Singh:
At least for the DMA-buf part feel free to add an Reviewed-by: Christian König christian.koenig@amd.com for this.
Regards, Christian.
On Wed, Jun 1, 2022 at 6:55 AM Christian König christian.koenig@amd.com wrote:
Thanks for the review, Christian.
--Kalesh
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...".
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.
Signed-off-by: Kalesh Singh kaleshsingh@google.com ---
Changes from rfc: - Split adding 'size' and 'path' into a separate patches, per Christian - Fix indentation (use tabs) in documentaion, per Randy
Documentation/filesystems/proc.rst | 14 ++++++++++++-- fs/proc/fd.c | 4 ++++ 2 files changed, 16 insertions(+), 2 deletions(-)
diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst index 779c05528e87..591f12d30d97 100644 --- a/Documentation/filesystems/proc.rst +++ b/Documentation/filesystems/proc.rst @@ -1886,14 +1886,16 @@ if precise results are needed. 3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file --------------------------------------------------------------- This file provides information associated with an opened file. The regular -files have at least five fields -- 'pos', 'flags', 'mnt_id', 'ino', and 'size'. +files have at least six fields -- 'pos', 'flags', 'mnt_id', 'ino', 'size', +and 'path'.
The 'pos' represents the current offset of the opened file in decimal form [see lseek(2) for details], 'flags' denotes the octal O_xxx mask the file has been created with [see open(2) for details] and 'mnt_id' represents mount ID of the file system containing the opened file [see 3.5 /proc/<pid>/mountinfo for details]. 'ino' represents the inode number of -the file, and 'size' represents the size of the file in bytes. +the file, 'size' represents the size of the file in bytes, and 'path' +represents the file path.
A typical output is::
@@ -1902,6 +1904,7 @@ A typical output is:: mnt_id: 19 ino: 63107 size: 0 + path: /dev/null
All locks associated with a file descriptor are shown in its fdinfo too::
@@ -1920,6 +1923,7 @@ 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. @@ -1934,6 +1938,7 @@ 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 @@ -1949,6 +1954,7 @@ 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, @@ -1968,6 +1974,7 @@ 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 @@ -1992,6 +1999,7 @@ 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 @@ -2018,6 +2026,7 @@ Timerfd files mnt_id: 9 ino: 63107 size: 0 + path: anon_inode:[timerfd] clockid: 0 ticks: 0 settime flags: 01 @@ -2042,6 +2051,7 @@ DMA Buffer files mnt_id: 9 ino: 63107 size: 32768 + path: /dmabuf: count: 2 exp_name: system-heap
diff --git a/fs/proc/fd.c b/fs/proc/fd.c index 464bc3f55759..8889a8ba09d4 100644 --- a/fs/proc/fd.c +++ b/fs/proc/fd.c @@ -60,6 +60,10 @@ static int seq_show(struct seq_file *m, void *v) 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_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); if (seq_has_overflowed(m))
On 5/31/22 14:25, Kalesh Singh wrote:
Hi Kalesh,
I think I see the value in the size field, but I'm curious about path, which is available via readlink /proc/<pid>/fd/<n>, since those are symlinks to the file themselves.
File paths can contain fun characters like newlines or colons, which could make parsing out filenames in this text file... fun. How would your userspace parsing logic handle "/home/stephen/filename\nsize:\t4096"? The readlink(2) API makes that easy already.
Is the goal avoiding races (e.g. file descriptor 3 is closed and reopened to a different path between reading fdinfo and stating the fd)?
Stephen
On Tue, May 31, 2022 at 3:07 PM Stephen Brennan stephen.s.brennan@oracle.com wrote:
Hi Stephen,
Thanks for taking a look.
This could work if we are root, but the file permissions wouldn't allow us to do the readlink on other processes otherwise. We want to be able to capture the system state in production environments from some trusted process with ptrace read capability.
I think since we have escaped the "\n" (seq_file_path(m, file, "\n")), then user space might parse this line like:
if (strncmp(line, "path:\t", 6) == 0) char* path = line + 6;
Thanks, Kalesh
Kalesh Singh kaleshsingh@google.com writes:
Interesting, thanks for explaining. It seems weird to have a duplicate interface for the same information but such is life.
I really should have read through that function before commenting, thanks for teaching me something new :)
Stephen
Am 01.06.22 um 00:48 schrieb Stephen Brennan:
Yeah, the size change is really straight forward but for this one I'm not 100% sure either.
Probably best to ping some core fs developer before going further with it.
BTW: Any preferred branch to push this upstream? If not I can take it through drm-misc-next.
Regards, Christian.
On Wed, Jun 1, 2022 at 8:02 AM Christian König ckoenig.leichtzumerken@gmail.com wrote:
The 2 concerns I think are: 1. Fun characters in the path names 2. If exposing the path is appropriate to begin with.
One way I think we can address both is to only expose the path for anon inodes. Then we have well-known path formats and we don't expose much about which files a process is accessing since these aren't real paths.
+ if (is_anon_inode(inode)) { + seq_puts(m, "path:\t"); + seq_file_path(m, file, "\n"); + seq_putc(m, '\n'); + }
Interested to hear thoughts on it.
Probably best to ping some core fs developer before going further with it.
linux-fsdevel is cc'd here. Adding Al Vrio as well. Please let me know if there are other parties I should include.
BTW: Any preferred branch to push this upstream? If not I can take it through drm-misc-next.
No other dependencies for this, so drm-misc-next is good.
Thanks, Kalesh
On Wed, Jun 1, 2022 at 8:31 PM Kalesh Singh kaleshsingh@google.com wrote:
Adding Christoph,
To be able to identify types of shared memory processes pin through FDs in production builds, we would like to add a 'path' field to fdinfo of anon inodes. We could then use the common prefixes ("/dmabuf", "/memfd", ...) to identify different types.
Would appreciate any feedback from the FS perspective.
Thanks, Kalesh
On Wed, Jun 15, 2022 at 10:00 AM Kalesh Singh kaleshsingh@google.com wrote:
Hi all,
If there are no objections to this, then I plan to respin the patch for just anonymous inodes. Please let me know if there are further concerns.
Thanks, Kalesh
From: Kalesh Singh
Sent: 31 May 2022 23:30
...
The real annoyance is other things doing scans of the filesystem that accidentally 'bump into' strange names.
While anything serious probably gets it right how many times Do you run 'find' to quickly search for something?
Spaces in filenames (popularised by some other os) are a PITA. Not to mention leading and trailing spaces! Anyone using filenames that only contain spaces does need shooting.
Deliberately adding non-printables isn't really a good idea.
David
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Christian König -
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