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authorGu Zheng <guz.fnst@cn.fujitsu.com>2013-10-25 12:15:06 +0200
committerAl Viro <viro@zeniv.linux.org.uk>2013-10-25 16:46:40 +0200
commit05e16745c0c471bba313961b605b6da3b21a853d (patch)
tree72d6432126a32d984dd8189942818df6d1a391ff /include/net/nfc/llc.h
parentnfsd regression since delayed fput() (diff)
downloadlinux-05e16745c0c471bba313961b605b6da3b21a853d.tar.xz
linux-05e16745c0c471bba313961b605b6da3b21a853d.zip
seq_file: always update file->f_pos in seq_lseek()
This issue was first pointed out by Jiaxing Wang several months ago, but no further comments: https://lkml.org/lkml/2013/6/29/41 As we know pread() does not change f_pos, so after pread(), file->f_pos and m->read_pos become different. And seq_lseek() does not update file->f_pos if offset equals to m->read_pos, so after pread() and seq_lseek()(lseek to m->read_pos), then a subsequent read may read from a wrong position, the following program produces the problem: char str1[32] = { 0 }; char str2[32] = { 0 }; int poffset = 10; int count = 20; /*open any seq file*/ int fd = open("/proc/modules", O_RDONLY); pread(fd, str1, count, poffset); printf("pread:%s\n", str1); /*seek to where m->read_pos is*/ lseek(fd, poffset+count, SEEK_SET); /*supposed to read from poffset+count, but this read from position 0*/ read(fd, str2, count); printf("read:%s\n", str2); out put: pread: ck_netbios_ns 12665 read: nf_conntrack_netbios /proc/modules: nf_conntrack_netbios_ns 12665 0 - Live 0xffffffffa038b000 nf_conntrack_broadcast 12589 1 nf_conntrack_netbios_ns, Live 0xffffffffa0386000 So we always update file->f_pos to offset in seq_lseek() to fix this issue. Signed-off-by: Jiaxing Wang <hello.wjx@gmail.com> Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'include/net/nfc/llc.h')
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