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procfs: /proc/pid/comm fixes

PATCH New Michał Mirosław 1 participant 3 messages Aug 31, 2017 Proc filesystem

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Michał Mirosław

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#0 lore raw

cover procfs: /proc/pid/comm fixes

These two patches are preparation for extending TASK_COMM_LEN above current 16-byte limit.

Michał Mirosław (2):
procfs: signal /proc/pid/comm write truncation
procfs: let userspace find out max /proc/pid/comm length

 fs/proc/base.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)
Signature · 1 line
2.11.0
author
#1 lore raw

PATCH 1/2 procfs: signal /proc/pid/comm write truncation

Keeps truncation working, but also signals to writing process when that happens.

Fixes 830e0fc967a7 ("fs, proc: truncate /proc/pid/comm writes to first TASK_COMM_LEN bytes")
Signed-off-by Michał Mirosław <[email protected]>
---
 fs/proc/base.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)
fs/proc/base.c +10 -1
index f1e1927ccd48..7238a64751e4 100644
@@ -1492,8 +1492,14 @@ static ssize_t comm_write(struct file *file, const char __user *buf,
 	char buffer[TASK_COMM_LEN];
 	const size_t maxlen = sizeof(buffer) - 1;
 
+	if (*offset)
+		return -ENOSPC;
+
+	if (count > maxlen)
+		count = maxlen;
+
 	memset(buffer, 0, sizeof(buffer));
-	if (copy_from_user(buffer, buf, count > maxlen ? maxlen : count))
+	if (copy_from_user(buffer, buf, count))
 		return -EFAULT;
 
 	p = get_proc_task(inode);

@@ -1507,6 +1513,9 @@ static ssize_t comm_write(struct file *file, const char __user *buf,
 
 	put_task_struct(p);
 
+	if (count > 0)
+		*offset = count;
+
 	return count;
 }
Signature · 1 line
2.11.0
author
#2 lore raw

PATCH 2/2 procfs: let userspace find out max /proc/pid/comm length

In reply to Michał Mirosław

Abuse llseek(SEEK_END) to return max /proc/pid/comm length.

This is needed for pthread_getname_np to be able to return ERANGE without modifying thread's name.

Signed-off-by Michał Mirosław <[email protected]>
---
 fs/proc/base.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)
fs/proc/base.c +10 -1
index 7238a64751e4..48089f087a8e 100644
@@ -1542,11 +1542,20 @@ static int comm_open(struct inode *inode, struct file *filp)
 	return single_open(filp, comm_show, inode);
 }
 
+static loff_t comm_lseek(struct file *file, loff_t offset, int whence)
+{
+	/* SEEK_END for seq_files normally gets -EINVAL */
+	if (whence == SEEK_END && offset == 0)
+		return TASK_COMM_LEN - 1;
+
+	return seq_lseek(file, offset, whence);
+}
+
 static const struct file_operations proc_pid_set_comm_operations = {
 	.open		= comm_open,
 	.read		= seq_read,
 	.write		= comm_write,
-	.llseek		= seq_lseek,
+	.llseek		= comm_lseek,
 	.release	= single_release,
 };
Signature · 1 line
2.11.0