From mboxrd@z Thu Jan 1 00:00:00 1970 From: Harsh Bora Subject: Re: [PATCH] Typecasting required for comparing unlike datatypes Date: Sun, 19 Dec 2010 12:32:27 +0530 Message-ID: <4D0DAE03.8000004@linux.vnet.ibm.com> References: <1291812900-18311-1-git-send-email-harsh@linux.vnet.ibm.com> <20101210171851.8f83f485.kamezawa.hiroyu@jp.fujitsu.com> <20101215095024.GH19804@ZenIV.linux.org.uk> <20101216092422.f0db600c.kamezawa.hiroyu@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: KAMEZAWA Hiroyuki , linux-fsdevel@vger.kernel.org, fengguang.wu@intel.com, aneesh.kumar@linux.vnet.ibm.com, jvrao@linux.vnet.ibm.com To: Al Viro Return-path: Received: from e23smtp01.au.ibm.com ([202.81.31.143]:47408 "EHLO e23smtp01.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751030Ab0LSHCe (ORCPT ); Sun, 19 Dec 2010 02:02:34 -0500 Received: from d23relay05.au.ibm.com (d23relay05.au.ibm.com [202.81.31.247]) by e23smtp01.au.ibm.com (8.14.4/8.13.1) with ESMTP id oBJ6x8H9007186 for ; Sun, 19 Dec 2010 17:59:08 +1100 Received: from d23av03.au.ibm.com (d23av03.au.ibm.com [9.190.234.97]) by d23relay05.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id oBJ72V7Q2043972 for ; Sun, 19 Dec 2010 18:02:31 +1100 Received: from d23av03.au.ibm.com (loopback [127.0.0.1]) by d23av03.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id oBJ72V0Z000310 for ; Sun, 19 Dec 2010 18:02:31 +1100 In-Reply-To: <20101216092422.f0db600c.kamezawa.hiroyu@jp.fujitsu.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On 12/16/2010 05:54 AM, KAMEZAWA Hiroyuki wrote: > On Wed, 15 Dec 2010 09:50:24 +0000 > Al Viro wrote: > >> On Fri, Dec 10, 2010 at 05:18:51PM +0900, KAMEZAWA Hiroyuki wrote: >>> On Wed, 8 Dec 2010 18:25:00 +0530 >>> Harsh Prateek Bora wrote: >>> >>>> The existing code causes the if condition to pass when it should fail >>>> on a *64-bit kernel* because of implicit data type conversions. It can >>>> be observed by passing pos = -1 and count = some positive number. >>>> This results in function returning EOVERFLOW instead of EINVAL. >>>> >>>> With this patch, the function returns EINVAL when pos is -1 and count >>>> is a positive number. This can be tested by calling sendfile with >>>> offset = -1 and count = some positive number on a 64-bit kernel. >>>> >>>> Signed-off-by: Harsh Prateek Bora >>> >>> Acked-by: KAMEZAWA Hiroyuki >>> >>> I'm sorry for annoying you. >> >> NAK. Look at what's getting done there; this check is the _only_ place >> in function that uses count, it is constantly false if count is zero >> _and_ we have only one caller that passes non-zero. Moreover, in case of >> count being zero we ignore offset as well. >> >> Obvious things to do: >> a) take the check in question into the only caller that would >> pass non-zero count (i.e. rw_verify_area()) >> b) lose the second and the third arguments of __negative_fpos_check() >> c) sort out what the hell should be done in that place. >> >> Note that current logics is very convoluted. First of all, we rely on >> loff_t being long long in the kernel and size_t being not bigger than >> unsigned long long. See ((loff_t)(pos + count)< 0) in there - if count >> gets wider than pos, we suddenly get all kinds of odd crap. >> >> That's OK; if we run into ports with size_t wider than 64 bits, we'll have >> more trouble anyway. >> >> So what we have for signed offset case is pos>= 0, count<= max loff_t - pos. >> Fair enough. For unsigned offset case it's more interesting - we want to >> allow pos< 0, and we just want to prohibit wraparounds from negative to >> positive. IOW, it's pos>= 0 || count< -pos; note that we already have >> count<= max ssize_t, which we assume to be no more than max loff_t. >> >> So what we need is this: >> if (unlikely(pos< 0)) { >> if it's signed >> -EINVAL >> if (count>= -pos) /* both values are in 0..LLONG_MAX */ >> -EOVERFLOW >> } else if (unlikely((loff_t)(pos + count)< 0)) { >> if it's signed >> -EINVAL >> } >> and we are done with that. IOW, how about the patch below? >> >> >> Signed-off-by: Al Viro > > This seems much easier to read. thank you. > > Acked-by: KAMEZAWA Hiroyuki > > and sorry for my 1st implemenation. > >> --- >> diff --git a/fs/read_write.c b/fs/read_write.c >> index 5d431ba..5520f8a 100644 >> --- a/fs/read_write.c >> +++ b/fs/read_write.c >> @@ -30,18 +30,9 @@ const struct file_operations generic_ro_fops = { >> >> EXPORT_SYMBOL(generic_ro_fops); >> >> -static int >> -__negative_fpos_check(struct file *file, loff_t pos, size_t count) >> +static inline int unsigned_offsets(struct file *file) >> { >> - /* >> - * 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; >> - if (file->f_mode& FMODE_UNSIGNED_OFFSET) >> - return 0; >> - return -EINVAL; >> + return file->f_mode& FMODE_UNSIGNED_OFFSET; >> } >> >> /** >> @@ -75,7 +66,7 @@ generic_file_llseek_unlocked(struct file *file, loff_t offset, int origin) >> break; >> } >> >> - if (offset< 0&& __negative_fpos_check(file, offset, 0)) >> + if (offset< 0&& !unsigned_offsets(file)) >> return -EINVAL; >> if (offset> inode->i_sb->s_maxbytes) >> return -EINVAL; >> @@ -152,7 +143,7 @@ loff_t default_llseek(struct file *file, loff_t offset, int origin) >> offset += file->f_pos; >> } >> retval = -EINVAL; >> - if (offset>= 0 || !__negative_fpos_check(file, offset, 0)) { >> + if (offset>= 0 || unsigned_offsets(file)) { >> if (offset != file->f_pos) { >> file->f_pos = offset; >> file->f_version = 0; >> @@ -252,9 +243,13 @@ int rw_verify_area(int read_write, struct file *file, loff_t *ppos, size_t count >> if (unlikely((ssize_t) count< 0)) >> return retval; >> pos = *ppos; >> - if (unlikely((pos< 0) || (loff_t) (pos + count)< 0)) { >> - retval = __negative_fpos_check(file, pos, count); >> - if (retval) >> + if (unlikely(pos< 0)) { >> + if (!unsigned_offsets(file)) >> + return retval; >> + if (count>= -pos) /* both values are in 0..LLONG_MAX */ Yeah .. thats a better reorg of code, however I am not sure if we need a typecast above for future portability reasons (as count and pos can be of diff width somewhere/sometime). Also, I personally would like to keep the function name as is_offset_unsigned(). Anyways, +1 for ACK ! Regards, Harsh >> + return -EOVERFLOW; >> + } else if (unlikely((loff_t) (pos + count)< 0)) { >> + if (!unsigned_offsets(file)) >> return retval; >> } >> >> > > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html