Hi Dan, On 2018/10/11 19:12, Dan Carpenter wrote: > On Thu, Oct 11, 2018 at 06:49:57PM +0800, Gao Xiang wrote: >> Hi Dan, >> >> On 2018/10/11 18:18, Dan Carpenter wrote: >>> On Thu, Oct 11, 2018 at 05:46:26PM +0800, Gao Xiang wrote: >>>> >>>> >>>> On 2018/10/11 16:44, Dan Carpenter wrote: >>>>> On Tue, Oct 09, 2018 at 10:07:13PM +0800, Gao Xiang wrote: >>>>>> This patch introduces inode hash function, test and set callbacks, >>>>>> and iget5_locked to find the right inode for 32-bit platforms. >>>>>> >>>>> >>>>> The way I read this changelog, we're trying to deal with corrupt file >>>>> systems? Is that correct? Presumably in the current code it could lead >>>>> to a Oops or something? >>>> >>>> No, this commit isn't trying to deal with corrupt file systems. >>>> In EROFS, the nid is not continuous and it represents the inode offset >>>> inode offset = nid * 32. >>>> Therefore the nid is 64-bit both for 32-bit and 64-bit platforms. However, >>>> i_ino is 'unsigned long', which means for 32-bit platforms, i_ino is not enough >>>> to contain the nid. >>>> >>>> Therefore, we should use iget5_locked for this case. >>> >>> I guess what I'm saying is, what are the user visible effects of this >>> patch? It's hard for me to tell from the patch description. Could you >>> please re-write the description and send a v2? >> >> Sorry for my just hurry reply. It seems I really misunderstood your point :-( >> >> If all nids are less than 32-bit, the user will see the correct inode/nid number >> for all 32-bit platforms, but if some nids are greater than 32-bit, it could be >> collisions without this patch for 32-bit platforms. >> >> This patch switch the inode number by XOR the high 32-bit and the low 32-bit, >> use customized tester to avoid collisions for 32-bit platforms. >> >> I will send v2 to fix the commit message...but it seems Greg is already merged in >> https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git/commit/?h=staging-testing&id=2abd7814138774eb56319e9dcc0abd08ece45424 >> > > Oh. Then that's fine then. If Greg already merged it, then it's too > late to change. Thanks for the explanation, though. I appended the v2 patch in the end of this reply for reference... Thanks, Gao Xiang > > regards, > dan carpenter > >From 175eb3f1c6e1cddf8292853ab0fb7644320c3ae2 Mon Sep 17 00:00:00 2001 From: Gao Xiang <gaoxiang25@xxxxxxxxxx> Date: Mon, 1 Oct 2018 12:32:55 +0800 Subject: [PATCH v2] staging: erofs: harden inode lookup for 32-bit platforms Each erofs inode has a unique 64-bit nid to distinguish from others. However, the inode number is usually defined as `unsigned long', which means some collisions could happen if we directly use iget_locked for 32-bit platforms. Therefore, this patch introduces a inode hash function, test and set callbacks, and iget5_locked to avoid potential collisions for 32-bit platforms. In addition, if the value of a nid is greater than 32-bit, users from 32-bit platforms will see XOR-ed inode numbers after this patch. Reviewed-by: Chao Yu <yuchao0@xxxxxxxxxx> Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx> --- change log v2: - add more infos to the commit message as pointed out by Dan Carpenter. Thanks, Gao Xiang drivers/staging/erofs/inode.c | 37 ++++++++++++++++++++++++++++++++++++- drivers/staging/erofs/internal.h | 9 +++++++++ 2 files changed, 45 insertions(+), 1 deletion(-) diff --git a/drivers/staging/erofs/inode.c b/drivers/staging/erofs/inode.c index da8693a7c3d3..04c61a9d7b76 100644 --- a/drivers/staging/erofs/inode.c +++ b/drivers/staging/erofs/inode.c @@ -232,10 +232,45 @@ static int fill_inode(struct inode *inode, int isdir) return err; } +/* + * erofs nid is 64bits, but i_ino is 'unsigned long', therefore + * we should do more for 32-bit platform to find the right inode. + */ +#if BITS_PER_LONG == 32 +static int erofs_ilookup_test_actor(struct inode *inode, void *opaque) +{ + const erofs_nid_t nid = *(erofs_nid_t *)opaque; + + return EROFS_V(inode)->nid == nid; +} + +static int erofs_iget_set_actor(struct inode *inode, void *opaque) +{ + const erofs_nid_t nid = *(erofs_nid_t *)opaque; + + inode->i_ino = erofs_inode_hash(nid); + return 0; +} +#endif + +static inline struct inode *erofs_iget_locked(struct super_block *sb, + erofs_nid_t nid) +{ + const unsigned long hashval = erofs_inode_hash(nid); + +#if BITS_PER_LONG >= 64 + /* it is safe to use iget_locked for >= 64-bit platform */ + return iget_locked(sb, hashval); +#else + return iget5_locked(sb, hashval, erofs_ilookup_test_actor, + erofs_iget_set_actor, &nid); +#endif +} + struct inode *erofs_iget(struct super_block *sb, erofs_nid_t nid, bool isdir) { - struct inode *inode = iget_locked(sb, nid); + struct inode *inode = erofs_iget_locked(sb, nid); if (unlikely(inode == NULL)) return ERR_PTR(-ENOMEM); diff --git a/drivers/staging/erofs/internal.h b/drivers/staging/erofs/internal.h index 5096b27bcf0d..57575c7f5635 100644 --- a/drivers/staging/erofs/internal.h +++ b/drivers/staging/erofs/internal.h @@ -517,6 +517,15 @@ erofs_get_inline_page(struct inode *inode, } /* inode.c */ +static inline unsigned long erofs_inode_hash(erofs_nid_t nid) +{ +#if BITS_PER_LONG == 32 + return (nid >> 32) ^ (nid & 0xffffffff); +#else + return nid; +#endif +} + extern struct inode *erofs_iget(struct super_block *sb, erofs_nid_t nid, bool dir); -- 2.14.4 _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
