Messages in this thread Patch in this message | | | Date | Sun, 24 Aug 2008 04:01:28 -0700 | From | Zev Weiss <> | Subject | Re: [PATCH] [MTD] mtdchar.c: Fix regression in MEMGETREGIONINFO ioctl() |
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Andrew Morton wrote: > On Sat, 23 Aug 2008 01:10:21 -0700 Zev Weiss <zevweiss@gmail.com> wrote: > >> Hmm. Well, I may be misunderstanding what you're saying (again, I'm very much >> a newbie to kernelspace), but I *think* the "copying four u32's out to >> userspace" thing isn't really a problem with my patch. It does certainly copy >> those four u32's, but given that `ur' (struct mtd_region_info_user) is >> initialized by copying from userspace, its fourth u32 (the `regionindex' >> member) should be identical when copied back out to userspace, given that it's >> not touched in the memberwise modification of the struct. > > OK, that's fortuitously bug-free in single-threaded userspace but > fantastically-improbably-buggy if userspace is threaded. > > But it's something the kernel shouldn't be doing. >
Ah, good point -- that hadn't occurred to me at all. Though it looks pretty clumsy/simpleminded to me, I guess something like this would avoid copying and rewriting the fourth u32 ("Well, duh" may be the appropriate response here):
diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c index 13cc67a..424f318 100644 --- a/drivers/mtd/mtdchar.c +++ b/drivers/mtd/mtdchar.c @@ -410,16 +410,20 @@ static int mtd_ioctl(struct inode *inode, struct file *file,
case MEMGETREGIONINFO: { - struct region_info_user ur; + u32 ur_idx; + struct mtd_erase_region_info *kr; + struct region_info_user *ur = (struct region_info_user *) argp;
- if (copy_from_user(&ur, argp, sizeof(struct region_info_user))) + if (get_user(ur_idx,&(ur->regionindex))) return -EFAULT;
- if (ur.regionindex >= mtd->numeraseregions) - return -EINVAL; - if (copy_to_user(argp, &(mtd->eraseregions[ur.regionindex]), - sizeof(struct mtd_erase_region_info))) + kr = &(mtd->eraseregions[ur_idx]); + + if (put_user(kr->offset, &(ur->offset)) + || put_user(kr->erasesize, &(ur->erasesize)) + || put_user(kr->numblocks, &(ur->numblocks))) return -EFAULT; + break; }
[Note: this is not even so much as compile-tested, and will remain that way until Monday, but I think you get the picture.]
>> So yes, it is >> copying 4 bytes more than is strictly necessary, but it seemed like a >> reasonably clean way of going about it (to me, for what that's worth). >> >> In my particular situation it didn't do anything unexpected in my testing (and >> restored the normal behavior I had when previously running 2.6.17.7). >> >> On the other hand, if I'm missing something completely, please let me know, >> and perhaps I can prepare a more suitable fix. > > "good enough" is never good enough ;) > > What is the ideal implementation? Let's implement that. > >
Well that, I'm afraid, is a question that I think would require somewhat greater depth of understanding than I possess (and I very much doubt the above patch is it). Given what you said earlier, it seems like the ideal solution would involve a reworking of the patch that added the `lockmap' member to struct mtd_erase_region_info, but I'm probably not the person to be messing around with that. So...anyone-who-knows-mtd-better-than-I, care to comment?
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