Commit 41662f5c authored by Kees Cook's avatar Kees Cook Committed by Linus Torvalds

sysctl: enable strict writes

SYSCTL_WRITES_WARN was added in commit f4aacea2 ("sysctl: allow for
strict write position handling"), and released in v3.16 in August of
2014.  Since then I can find only 1 instance of non-zero offset
writing[1], and it was fixed immediately in CRIU[2].  As such, it
appears safe to flip this to the strict state now.

[1] https://www.google.com/search?q="when%20file%20position%20was%20not%200"
[2] http://lists.openvz.org/pipermail/criu/2015-April/019819.htmlSigned-off-by: default avatarKees Cook <keescook@chromium.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a460bece
...@@ -825,14 +825,13 @@ via the /proc/sys interface: ...@@ -825,14 +825,13 @@ via the /proc/sys interface:
Each write syscall must fully contain the sysctl value to be Each write syscall must fully contain the sysctl value to be
written, and multiple writes on the same sysctl file descriptor written, and multiple writes on the same sysctl file descriptor
will rewrite the sysctl value, regardless of file position. will rewrite the sysctl value, regardless of file position.
0 - (default) Same behavior as above, but warn about processes that 0 - Same behavior as above, but warn about processes that perform writes
perform writes to a sysctl file descriptor when the file position to a sysctl file descriptor when the file position is not 0.
is not 0. 1 - (default) Respect file position when writing sysctl strings. Multiple
1 - Respect file position when writing sysctl strings. Multiple writes writes will append to the sysctl value buffer. Anything past the max
will append to the sysctl value buffer. Anything past the max length length of the sysctl value buffer will be ignored. Writes to numeric
of the sysctl value buffer will be ignored. Writes to numeric sysctl sysctl entries must always be at file position 0 and the value must
entries must always be at file position 0 and the value must be be fully contained in the buffer sent in the write syscall.
fully contained in the buffer sent in the write syscall.
============================================================== ==============================================================
......
...@@ -173,7 +173,7 @@ extern int no_unaligned_warning; ...@@ -173,7 +173,7 @@ extern int no_unaligned_warning;
#define SYSCTL_WRITES_WARN 0 #define SYSCTL_WRITES_WARN 0
#define SYSCTL_WRITES_STRICT 1 #define SYSCTL_WRITES_STRICT 1
static int sysctl_writes_strict = SYSCTL_WRITES_WARN; static int sysctl_writes_strict = SYSCTL_WRITES_STRICT;
static int proc_do_cad_pid(struct ctl_table *table, int write, static int proc_do_cad_pid(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp, loff_t *ppos); void __user *buffer, size_t *lenp, loff_t *ppos);
......
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