Messages in this thread Patch in this message | | | Date | Thu, 17 Sep 2009 16:23:24 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [RFC][PATCH][bugfix] more checks for negative f_pos handling v4 |
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On Thu, 17 Sep 2009 15:14:28 +0800 Wu Fengguang <fengguang.wu@intel.com> wrote:
> On Thu, Sep 17, 2009 at 02:51:00PM +0800, KAMEZAWA Hiroyuki wrote: > > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> > > > > Now, rw_verify_area() checsk f_pos is negative or not. And if > > negative, returns -EINVAL. > > > > But, some special files as /dev/(k)mem and /proc/<pid>/mem etc.. > > has negative offsets. And we can't do any access via read/write > > to the file(device). > > > > This patch introduce a flag S_VERYBIG and allow negative file > > offsets for big files. (usual files don't allow it.) > > > > Changelog: v3->v4 > > - make changes in mem.c aligned. > > - change __negative_fpos_check() to return int. > > - fixed bug in "pos" check. > > - added comments. > > > > Changelog: v2->v3 > > - fixed bug in rw_verify_area (it cannot be compiled) > > > > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> > > --- > > drivers/char/mem.c | 23 +++++++++++++---------- > > fs/proc/base.c | 2 ++ > > fs/read_write.c | 22 ++++++++++++++++++++-- > > include/linux/fs.h | 2 ++ > > 4 files changed, 37 insertions(+), 12 deletions(-) > > > > Index: mmotm-2.6.31-Sep14/fs/read_write.c > > =================================================================== > > --- mmotm-2.6.31-Sep14.orig/fs/read_write.c > > +++ mmotm-2.6.31-Sep14/fs/read_write.c > > @@ -205,6 +205,21 @@ bad: > > } > > #endif > > > > +static int > > +__negative_fpos_check(struct inode *inode, loff_t pos, size_t count) > > +{ > > + /* > > + * pos or pos+count is negative here, check overflow. > > + * too big "count" will be caught in rw_verify_area(). > > + */ > > + if ((pos < 0) && (pos + count < pos)) > > + return -EOVERFLOW; > > This returns -EOVERFLOW when pos=-10 and count=1. What's the intention? Hmm ?
pos+count=-9 > -10 ? it's ok. no -EOVERFLOW
pos=-10, count=11, pos+count=1 > -10, then overflow.
> Just to return a different error code other than -EINVAL? > For showing what this "if" checks. EINVAL is better ?
Thanks, -Kame
> Also it seems you did two behavior changes at the same time: the above > -EOVERFLOW and the below IS_VERYBIG(). Are they tightly coupled? > > > + /* If !VERYBIG inode, negative pos(pos+count) is not allowed */ > > + if (!IS_VERYBIG(inode)) > > + return -EINVAL; > > + return 0; > > +} > > + > > /* > > * rw_verify_area doesn't like huge counts. We limit > > * them to something that fits in "int" so that others > > @@ -222,8 +237,11 @@ int rw_verify_area(int read_write, struc > > if (unlikely((ssize_t) count < 0)) > > return retval; > > pos = *ppos; > > - if (unlikely((pos < 0) || (loff_t) (pos + count) < 0)) > > - return retval; > > + if (unlikely((pos < 0) || (loff_t) (pos + count) < 0)) { > > + retval = __negative_fpos_check(inode, pos, count); > > + if (retval) > > + return retval; > > + } > > This could look more nicer: > > retval = __negative_fpos_check(inode, pos, count); > if (retval) > return retval; > > But they are all minor issues :) > > Thanks, > Fengguang > > > > > if (unlikely(inode->i_flock && mandatory_lock(inode))) { > > retval = locks_mandatory_area( > > Index: mmotm-2.6.31-Sep14/include/linux/fs.h > > =================================================================== > > --- mmotm-2.6.31-Sep14.orig/include/linux/fs.h > > +++ mmotm-2.6.31-Sep14/include/linux/fs.h > > @@ -231,6 +231,7 @@ struct inodes_stat_t { > > #define S_NOCMTIME 128 /* Do not update file c/mtime */ > > #define S_SWAPFILE 256 /* Do not truncate: swapon got its bmaps */ > > #define S_PRIVATE 512 /* Inode is fs-internal */ > > +#define S_VERYBIG 1024 /* Allow file's loff_t can be negative */ > > > > /* > > * Note that nosuid etc flags are inode-specific: setting some file-system > > @@ -265,6 +266,7 @@ struct inodes_stat_t { > > #define IS_NOCMTIME(inode) ((inode)->i_flags & S_NOCMTIME) > > #define IS_SWAPFILE(inode) ((inode)->i_flags & S_SWAPFILE) > > #define IS_PRIVATE(inode) ((inode)->i_flags & S_PRIVATE) > > +#define IS_VERYBIG(inode) ((inode)->i_flags & S_VERYBIG) > > > > /* the read-only stuff doesn't really belong here, but any other place is > > probably as bad and I don't want to create yet another include file. */ > > Index: mmotm-2.6.31-Sep14/drivers/char/mem.c > > =================================================================== > > --- mmotm-2.6.31-Sep14.orig/drivers/char/mem.c > > +++ mmotm-2.6.31-Sep14/drivers/char/mem.c > > @@ -825,22 +825,23 @@ static const struct memdev { > > const char *name; > > const struct file_operations *fops; > > struct backing_dev_info *dev_info; > > + bool verybig; > > } devlist[] = { > > - [ 1] = { "mem", &mem_fops, &directly_mappable_cdev_bdi }, > > + [1] = { "mem", &mem_fops, &directly_mappable_cdev_bdi, true }, > > #ifdef CONFIG_DEVKMEM > > - [ 2] = { "kmem", &kmem_fops, &directly_mappable_cdev_bdi }, > > + [2] = { "kmem", &kmem_fops, &directly_mappable_cdev_bdi, true }, > > #endif > > - [ 3] = {"null", &null_fops, NULL }, > > + [3] = {"null", &null_fops, NULL, false }, > > #ifdef CONFIG_DEVPORT > > - [ 4] = { "port", &port_fops, NULL }, > > + [4] = { "port", &port_fops, NULL, false }, > > #endif > > - [ 5] = { "zero", &zero_fops, &zero_bdi }, > > - [ 6] = { "full", &full_fops, NULL }, > > - [ 7] = { "random", &random_fops, NULL }, > > - [ 9] = { "urandom", &urandom_fops, NULL }, > > - [11] = { "kmsg", &kmsg_fops, NULL }, > > + [5] = { "zero", &zero_fops, &zero_bdi, false }, > > + [6] = { "full", &full_fops, NULL, false }, > > + [7] = { "random", &random_fops, NULL, false }, > > + [9] = { "urandom", &urandom_fops, NULL, false }, > > + [11] = { "kmsg", &kmsg_fops, NULL, false }, > > #ifdef CONFIG_CRASH_DUMP > > - [12] = { "oldmem", &oldmem_fops, NULL }, > > + [12] = { "oldmem", &oldmem_fops, NULL, false }, > > #endif > > }; > > > > @@ -868,6 +869,8 @@ static int memory_open(struct inode *ino > > ret = dev->fops->open(inode, filp); > > else > > ret = 0; > > + if (dev->verybig) > > + inode->i_flags |= S_VERYBIG; > > out: > > unlock_kernel(); > > return ret; > > Index: mmotm-2.6.31-Sep14/fs/proc/base.c > > =================================================================== > > --- mmotm-2.6.31-Sep14.orig/fs/proc/base.c > > +++ mmotm-2.6.31-Sep14/fs/proc/base.c > > @@ -779,6 +779,8 @@ static const struct file_operations proc > > static int mem_open(struct inode* inode, struct file* file) > > { > > file->private_data = (void*)((long)current->self_exec_id); > > + /* this file is read only and we can catch out-pf-range */ > > + inode->i_flags |= S_VERYBIG; > > return 0; > > } > > >
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