The patch titled
Subject: fs, proc: truncate /proc/pid/comm writes to first TASK_COMM_LEN bytes
has been added to the -mm tree. Its filename is
fs-proc-truncate-proc-pid-comm-writes-to-first-task_comm_len-bytes.patch
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------------------------------------------------------
From: David Rientjes <rientjes@xxxxxxxxxx>
Subject: fs, proc: truncate /proc/pid/comm writes to first TASK_COMM_LEN bytes
Currently, a write to a procfs file will return the number of bytes
successfully written. If the actual string is longer than this, the
remainder of the string will not be be written and userspace will complete
the operation by issuing additional write()s.
Hence
$ echo -n "abcdefghijklmnopqrs" > /proc/self/comm
results in
$ cat /proc/$$/comm
pqrs
since the final four bytes were written with a second write() since
TASK_COMM_LEN == 16. This is obviously an undesired result and not
equivalent to prctl(PR_SET_NAME). The implementation should not need to
know the definition of TASK_COMM_LEN.
This patch truncates the string to the first TASK_COMM_LEN bytes and
returns the bytes written as the length of the string written so the
second write() is suppressed.
$ cat /proc/$$/comm
abcdefghijklmno
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/proc/base.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff -puN fs/proc/base.c~fs-proc-truncate-proc-pid-comm-writes-to-first-task_comm_len-bytes fs/proc/base.c
--- a/fs/proc/base.c~fs-proc-truncate-proc-pid-comm-writes-to-first-task_comm_len-bytes
+++ a/fs/proc/base.c
@@ -1347,11 +1347,10 @@ static ssize_t comm_write(struct file *f
struct inode *inode = file_inode(file);
struct task_struct *p;
char buffer[TASK_COMM_LEN];
+ const size_t maxlen = sizeof(buffer) - 1;
memset(buffer, 0, sizeof(buffer));
- if (count > sizeof(buffer) - 1)
- count = sizeof(buffer) - 1;
- if (copy_from_user(buffer, buf, count))
+ if (copy_from_user(buffer, buf, count > maxlen ? maxlen : count))
return -EFAULT;
p = get_proc_task(inode);
_
Patches currently in -mm which might be from rientjes@xxxxxxxxxx are
linux-next.patch
mm-show_mem-suppress-page-counts-in-non-blockable-contexts.patch
mm-hugetlb-include-hugepages-in-meminfo.patch
mm-hugetlb-include-hugepages-in-meminfo-checkpatch-fixes.patch
mm-speedup-in-__early_pfn_to_nid.patch
mm-speedup-in-__early_pfn_to_nid-fix.patch
thp-fix-comment-about-memory-barrier.patch
mm-dmapoolc-fix-null-dev-in-dma_pool_create.patch
fs-proc-truncate-proc-pid-comm-writes-to-first-task_comm_len-bytes.patch
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