Messages in this thread Patch in this message | | | From | Joe Lawrence <> | Subject | [PATCH 3/3] pipe: add proc_dopipe_max_size() to safely assign pipe_max_size | Date | Tue, 26 Sep 2017 10:21:24 -0400 |
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pipe_max_size is assigned directly via procfs sysctl:
static struct ctl_table fs_table[] = { ... { .procname = "pipe-max-size", .data = &pipe_max_size, .maxlen = sizeof(int), .mode = 0644, .proc_handler = &pipe_proc_fn, .extra1 = &pipe_min_size, }, ...
int pipe_proc_fn(struct ctl_table *table, int write, void __user *buf, size_t *lenp, loff_t *ppos) { ... ret = proc_dointvec_minmax(table, write, buf, lenp, ppos) ...
and then later rounded in-place a few statements later:
... pipe_max_size = round_pipe_size(pipe_max_size); ...
This leaves a window of time between initial assignment and rounding that may be visible to other threads. (For example, one thread sets a non-rounded value to pipe_max_size while another reads its value.)
Similar reads of pipe_max_size are potentially racey:
pipe.c :: alloc_pipe_info() pipe.c :: pipe_set_size()
Add a new proc_dopipe_max_size() function that consolidates reading the new value from the user buffer, verifying bounds, and calling round_pipe_size() with a single assignment to pipe_max_size.
Reported-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com> --- fs/pipe.c | 16 ++-------------- include/linux/pipe_fs_i.h | 1 + include/linux/sysctl.h | 3 +++ kernel/sysctl.c | 43 +++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 49 insertions(+), 14 deletions(-)
diff --git a/fs/pipe.c b/fs/pipe.c index 8cbc97d97753..4db3cd2d139c 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -1019,7 +1019,7 @@ static int fifo_open(struct inode *inode, struct file *filp) * Currently we rely on the pipe array holding a power-of-2 number * of pages. Returns 0 on error. */ -static inline unsigned int round_pipe_size(unsigned int size) +unsigned int round_pipe_size(unsigned int size) { unsigned long nr_pages; @@ -1130,19 +1130,7 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg) int pipe_proc_fn(struct ctl_table *table, int write, void __user *buf, size_t *lenp, loff_t *ppos) { - unsigned int rounded_pipe_max_size; - int ret; - - ret = proc_douintvec_minmax(table, write, buf, lenp, ppos); - if (ret < 0 || !write) - return ret; - - rounded_pipe_max_size = round_pipe_size(pipe_max_size); - if (rounded_pipe_max_size == 0) - return -EINVAL; - - pipe_max_size = rounded_pipe_max_size; - return ret; + return proc_dopipe_max_size(table, write, buf, lenp, ppos); } /* diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h index e7497c9dde7f..485cf7a7aa8f 100644 --- a/include/linux/pipe_fs_i.h +++ b/include/linux/pipe_fs_i.h @@ -190,5 +190,6 @@ static inline int pipe_buf_steal(struct pipe_inode_info *pipe, struct pipe_inode_info *get_pipe_info(struct file *file); int create_pipe_files(struct file **, int); +unsigned int round_pipe_size(unsigned int size); #endif diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h index 1d4dba490fb6..ba24ca72800c 100644 --- a/include/linux/sysctl.h +++ b/include/linux/sysctl.h @@ -50,6 +50,9 @@ extern int proc_dointvec_minmax(struct ctl_table *, int, extern int proc_douintvec_minmax(struct ctl_table *table, int write, void __user *buffer, size_t *lenp, loff_t *ppos); +extern int proc_dopipe_max_size(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, + loff_t *ppos); extern int proc_dointvec_jiffies(struct ctl_table *, int, void __user *, size_t *, loff_t *); extern int proc_dointvec_userhz_jiffies(struct ctl_table *, int, diff --git a/kernel/sysctl.c b/kernel/sysctl.c index c976719bf37a..7a2913c5546e 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -67,6 +67,7 @@ #include <linux/kexec.h> #include <linux/bpf.h> #include <linux/mount.h> +#include <linux/pipe_fs_i.h> #include <linux/uaccess.h> #include <asm/processor.h> @@ -2631,6 +2632,47 @@ int proc_douintvec_minmax(struct ctl_table *table, int write, do_proc_douintvec_minmax_conv, ¶m); } +struct do_proc_dopipe_max_size_conv_param { + unsigned int *min; +}; + +static int do_proc_dopipe_max_size_conv(unsigned long *lvalp, + unsigned int *valp, + int write, void *data) +{ + struct do_proc_dopipe_max_size_conv_param *param = data; + + if (write) { + unsigned int val = round_pipe_size(*lvalp); + + if (val == 0) + return -EINVAL; + + if (param->min && *param->min > val) + return -ERANGE; + + if (*lvalp > UINT_MAX) + return -EINVAL; + + *valp = val; + } else { + unsigned int val = *valp; + *lvalp = (unsigned long) val; + } + + return 0; +} + +int proc_dopipe_max_size(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, loff_t *ppos) +{ + struct do_proc_dopipe_max_size_conv_param param = { + .min = (unsigned int *) table->extra1, + }; + return do_proc_douintvec(table, write, buffer, lenp, ppos, + do_proc_dopipe_max_size_conv, ¶m); +} + static void validate_coredump_safety(void) { #ifdef CONFIG_COREDUMP @@ -3179,6 +3221,7 @@ int proc_doulongvec_ms_jiffies_minmax(struct ctl_table *table, int write, EXPORT_SYMBOL(proc_dointvec_jiffies); EXPORT_SYMBOL(proc_dointvec_minmax); EXPORT_SYMBOL_GPL(proc_douintvec_minmax); +EXPORT_SYMBOL_GPL(proc_dopipe_max_size); EXPORT_SYMBOL(proc_dointvec_userhz_jiffies); EXPORT_SYMBOL(proc_dointvec_ms_jiffies); EXPORT_SYMBOL(proc_dostring); -- 1.8.3.1
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