Messages in this thread | | | Date | Wed, 1 Jun 2022 17:02:11 +0200 | Subject | Re: [Linaro-mm-sig] Re: [PATCH 2/2] procfs: Add 'path' to /proc/<pid>/fdinfo/ | From | Christian König <> |
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Am 01.06.22 um 00:48 schrieb Stephen Brennan: > Kalesh Singh <kaleshsingh@google.com> writes: >> On Tue, May 31, 2022 at 3:07 PM Stephen Brennan >> <stephen.s.brennan@oracle.com> wrote: >>> On 5/31/22 14:25, Kalesh Singh wrote: >>>> 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. >>> Hi Kalesh, >> Hi Stephen, >> >> Thanks for taking a look. >> >>> 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. >> 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. > Interesting, thanks for explaining. It seems weird to have a duplicate > interface for the same information but such is life.
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.
> >>> 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. >> I think since we have escaped the "\n" (seq_file_path(m, file, "\n")), > I really should have read through that function before commenting, > thanks for teaching me something new :) > > Stephen > >> then user space might parse this line like: >> >> if (strncmp(line, "path:\t", 6) == 0) >> char* path = line + 6; >> >> >> Thanks, >> Kalesh >> >>> 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 >>> >>>> 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)) >>> -- >>> To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. >>> > _______________________________________________ > Linaro-mm-sig mailing list -- linaro-mm-sig@lists.linaro.org > To unsubscribe send an email to linaro-mm-sig-leave@lists.linaro.org
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