4.18-stable review patch. If anyone has any objections, please let me know.
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From: Aurelien Aptel aaptel@suse.com
commit 0595751f267994c3c7027377058e4185b3a28e75 upstream.
When mounting a Windows share that is the root of a drive (eg. C$) the server does not return . and .. directory entries. This results in the smb2 code path erroneously skipping the 2 first entries.
Pseudo-code of the readdir() code path:
cifs_readdir(struct file, struct dir_context) initiate_cifs_search <-- if no reponse cached yet server->ops->query_dir_first
dir_emit_dots dir_emit <-- adds "." and ".." if we're at pos=0
find_cifs_entry initiate_cifs_search <-- if pos < start of current response (restart search) server->ops->query_dir_next <-- if pos > end of current response (fetch next search res)
for(...) <-- loops over cur response entries starting at pos cifs_filldir <-- skip . and .., emit entry cifs_fill_dirent dir_emit pos++
A) dir_emit_dots() always adds . & .. and sets the current dir pos to 2 (0 and 1 are done).
Therefore we always want the index_to_find to be 2 regardless of if the response has . and ..
B) smb1 code initializes index_of_last_entry with a +2 offset
in cifssmb.c CIFSFindFirst(): psrch_inf->index_of_last_entry = 2 /* skip . and .. */ + psrch_inf->entries_in_buffer;
Later in find_cifs_entry() we want to find the next dir entry at pos=2 as a result of (A)
first_entry_in_buffer = cfile->srch_inf.index_of_last_entry - cfile->srch_inf.entries_in_buffer;
This var is the dir pos that the first entry in the buffer will have therefore it must be 2 in the first call.
If we don't offset index_of_last_entry by 2 (like in (B)), first_entry_in_buffer=0 but we were instructed to get pos=2 so this code in find_cifs_entry() skips the 2 first which is ok for non-root shares, as it skips . and .. from the response but is not ok for root shares where the 2 first are actual files
pos_in_buf = index_to_find - first_entry_in_buffer; // pos_in_buf=2 // we skip 2 first response entries :( for (i = 0; (i < (pos_in_buf)) && (cur_ent != NULL); i++) { /* go entry by entry figuring out which is first */ cur_ent = nxt_dir_entry(cur_ent, end_of_smb, cfile->srch_inf.info_level); }
C) cifs_filldir() skips . and .. so we can safely ignore them for now.
Sample program:
int main(int argc, char **argv) { const char *path = argc >= 2 ? argv[1] : "."; DIR *dh; struct dirent *de;
printf("listing path <%s>\n", path); dh = opendir(path); if (!dh) { printf("opendir error %d\n", errno); return 1; }
while (1) { de = readdir(dh); if (!de) { if (errno) { printf("readdir error %d\n", errno); return 1; } printf("end of listing\n"); break; } printf("off=%lu <%s>\n", de->d_off, de->d_name); }
return 0; }
Before the fix with SMB1 on root shares:
<.> off=1 <..> off=2 <$Recycle.Bin> off=3 <bootmgr> off=4
and on non-root shares:
<.> off=1 <..> off=4 <-- after adding .., the offsets jumps to +2 because <2536> off=5 we skipped . and .. from response buffer (C) <411> off=6 but still incremented pos <file> off=7 <fsx> off=8
Therefore the fix for smb2 is to mimic smb1 behaviour and offset the index_of_last_entry by 2.
Test results comparing smb1 and smb2 before/after the fix on root share, non-root shares and on large directories (ie. multi-response dir listing):
PRE FIX ======= pre-1-root VS pre-2-root: ERR pre-2-root is missing [bootmgr, $Recycle.Bin] pre-1-nonroot VS pre-2-nonroot: OK~ same files, same order, different offsets pre-1-nonroot-large VS pre-2-nonroot-large: OK~ same files, same order, different offsets
POST FIX ======== post-1-root VS post-2-root: OK same files, same order, same offsets post-1-nonroot VS post-2-nonroot: OK same files, same order, same offsets post-1-nonroot-large VS post-2-nonroot-large: OK same files, same order, same offsets
REGRESSION? =========== pre-1-root VS post-1-root: OK same files, same order, same offsets pre-1-nonroot VS post-1-nonroot: OK same files, same order, same offsets
BugLink: https://bugzilla.samba.org/show_bug.cgi?id=13107 Signed-off-by: Aurelien Aptel aaptel@suse.com Signed-off-by: Paulo Alcantara palcantara@suse.deR Reviewed-by: Ronnie Sahlberg lsahlber@redhat.com Signed-off-by: Steve French stfrench@microsoft.com CC: Stable stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/cifs/smb2ops.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/fs/cifs/smb2ops.c +++ b/fs/cifs/smb2ops.c @@ -1484,7 +1484,7 @@ smb2_query_dir_first(const unsigned int }
srch_inf->entries_in_buffer = 0; - srch_inf->index_of_last_entry = 0; + srch_inf->index_of_last_entry = 2;
rc = SMB2_query_directory(xid, tcon, fid->persistent_fid, fid->volatile_fid, 0, srch_inf);