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cifs: fix sb->s_maxbytes so that it casts properly to a signed value
This off-by-one bug causes sendfile() to not work properly. When a task calls sendfile() on a file on a CIFS filesystem, the syscall returns -1 and sets errno to EOVERFLOW. do_sendfile uses s_maxbytes to verify the returned offset of the file. The problem there is that this value is cast to a signed value (loff_t). When this is done on the s_maxbytes value that cifs uses, it becomes negative and the comparisons against it fail. Even though s_maxbytes is an unsigned value, it seems that it's not OK to set it in such a way that it'll end up negative when it's cast to a signed value. These casts happen in other codepaths besides sendfile too, but the VFS is a little hard to follow in this area and I can't be sure if there are other bugs that this will fix. It's not clear to me why s_maxbytes isn't just declared as loff_t in the first place, but either way we still need to fix these values to make sendfile work properly. This is also an opportunity to replace the magic bit-shift values here with the standard #defines for this. This fixes the reproducer program I have that does a sendfile and will probably also fix the situation where apache is serving from a CIFS share. Acked-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Jeff Layton <jlayton@redhat.com> Signed-off-by: Steve French <sfrench@us.ibm.com>
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1 changed files with 4 additions and 4 deletions
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@ -2452,10 +2452,10 @@ cifs_mount(struct super_block *sb, struct cifs_sb_info *cifs_sb,
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tcon->local_lease = volume_info->local_lease;
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}
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if (pSesInfo) {
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if (pSesInfo->capabilities & CAP_LARGE_FILES) {
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sb->s_maxbytes = (u64) 1 << 63;
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} else
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sb->s_maxbytes = (u64) 1 << 31; /* 2 GB */
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if (pSesInfo->capabilities & CAP_LARGE_FILES)
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sb->s_maxbytes = MAX_LFS_FILESIZE;
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else
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sb->s_maxbytes = MAX_NON_LFS;
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}
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/* BB FIXME fix time_gran to be larger for LANMAN sessions */
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